Training for Your First Marathon: The Complete Guide — From First Steps to Finish Line
- 20 hours ago
- 18 min read
Written by Andy Hood — ultra and endurance runner, cancer survivor, and the voice behind runningwestwardho.co.uk. Andy has completed multiple ultras including a 170-mile run to Land's End on the South West Coast Path and two finishes of the 160KM Tour du Mont Blanc.
Whether you're lacing up for the very first time or stepping up from a 10K or half marathon, training for your first marathon is one of the most rewarding, and challenging, things you'll ever do. This guide covers everything you need to know: training, fuelling, the mental game, how your body adapts, and the golden rules that will keep you healthy all the way to race day.
In this Article
So You've Decided to Run a Marathon
26.2 miles. 42.2 kilometres. It's a number that can feel either thrilling or terrifying depending on where you're starting from, and honestly, a bit of both is perfectly normal.
The marathon is unique. It's long enough to demand real respect in how you train and fuel, yet accessible enough that runners of every background and ability level cross the finish line every single year. The person who ran their first 5K eighteen months ago and the experienced half marathoner stepping up in distance are both capable of getting there. The path just looks a little different.
I've been running for years, ultras, multi-day endurance events, the South West Coast Path, the Tour du Mont Blanc, and looking back, every single mile has taught me something. The marathon distance sits at an interesting crossroads: long enough to test you, short enough (by ultra standards!) that with proper preparation, your body and mind can genuinely be ready for it. What I've learned across hundreds of miles and some very hard days is that the fundamentals never change, whether you're chasing 26 miles or 100.
This guide is built on those fundamentals.
Where Are You Starting From?
Before anything else, it helps to be honest about your starting point, not to limit yourself, but to plan intelligently.
Complete Beginners to Running
If you're new to running entirely, your first goal before committing to a marathon training plan is building a consistent running base. You don't need to have run a 5K or 10K first, but you do need to be running comfortably and regularly, ideally 3–4 times per week with some runs hitting the 30–45 minute mark without stopping, before marathon-specific training begins.
A Couch to 5K programme is a brilliant starting point if you're truly at zero. Give yourself time. There's no shame in spending three to six months building that base before the marathon plan kicks in. The runners who get injured or burn out are almost always the ones who rushed this part.
Stepping Up from a 10K
You have a solid foundation, you understand effort, you know what it feels like to push through the final kilometres of a race, and you've got a training routine. Now you're doubling the distance (and then some). The biggest shift isn't just in mileage, it's in time on your feet, which changes everything from how you fuel to how your legs recover. Your training plan needs to respect this transition. Don't assume that 10K fitness automatically carries you further without a structured build.
Stepping Up from a Half Marathon
This is arguably the most common route, and a smart one. You understand long runs, you've likely done back-to-back training weeks, and you have some experience of race-day nerves and strategy. But the jump from 13.1 to 26.2 miles is still a significant step, particularly beyond mile 18–20 where the race truly begins. Half marathon training doesn't fully prepare the body for what comes in the final third of a marathon, that preparation has to be built deliberately.
The Golden Rule: The 10% Principle
Whatever your starting point, the most important rule in marathon training, and in running more broadly, is this:
Never increase your weekly mileage or training effort by more than 10% from one week to the next.
It sounds almost too simple. It's not. This rule exists because the body adapts to running stress, but it does so on its own schedule. Your cardiovascular system improves relatively quickly. Your muscles, tendons, ligaments, and bones take significantly longer. That mismatch is where injuries happen, when your lungs feel like they can handle more, but your connective tissue hasn't caught up yet.
So if you're running 30 miles per week, your next week should cap out at around 33 miles. Not 40. Not 35 because you felt great. 33, then assess.
Build weeks are followed by recovery weeks. Most good marathon plans include a scheduled step-back every third or fourth week, dropping mileage by 20–30% to allow the body to absorb the training load before building again. These are not optional. They're where the adaptation actually happens.
I've learned this the hard way. The miles that feel easy to add are always the ones that come back to bite you. Respect the 10% rule, especially in the first half of your training block.
Building a Training Plan That Works
A standard first-marathon training plan runs 16–20 weeks. Here's the broad structure:
Weeks 1–4: Foundation. Establishing consistency, building base mileage gently, getting used to running 4–5 days per week.
Weeks 5–10: Development. Weekly mileage increases steadily. The long run begins to grow meaningfully, from 10 miles up towards 16–18. This is where easy running matters most.
Weeks 11–16: Peak. The longest training runs (typically 18–22 miles for most plans). Nutritional strategies get tested. Fatigue increases but so does confidence.
Weeks 17–20 (or final 2–3 weeks): Taper. Mileage drops significantly. You're not losing fitness, you're letting your body arrive at the start line recovered and sharp. Trust it, even when it feels strange. Browse Instagram and you'll see plenty of posts about the Taper Tantrums.
Easy Runs Are Not Junk Miles
One of the most common mistakes first-time marathon runners make is running their easy runs too fast. Easy runs should be genuinely easy, conversational pace, where you could hold a full sentence without gasping. These aren't throwaway miles. They build aerobic capacity, promote recovery between harder sessions, and accumulate the time on feet that marathon training demands.
A rough guide: around 80% of your training mileage should feel comfortable. Only 20% should involve genuine effort.
Check out this blog post about on Zone 2 traning
How Your Body Responds to Marathon Training
Training for a marathon puts stresses on the body that most people haven't experienced before. Understanding what's happening helps you respond intelligently rather than panic.
In the early weeks, you might feel surprisingly energetic. The training volume isn't yet high enough to fatigue you deeply. Enjoy it, but don't use it as an excuse to do more.
Around weeks 4–8, cumulative fatigue starts to set in. Legs may feel heavy. Sleep needs increase. This is normal and is the body signalling that it's working hard. This is exactly where the 10% rule matters.
As long runs extend beyond 16 miles, you're likely to encounter muscle soreness in places you haven't felt before, hip flexors, glutes, the outside of the knee. Your body is adapting its musculoskeletal structure to sustain prolonged effort, and that process takes time. I was talking to my sports physio at the gym recently and he made an observation that stuck with me: the most common point he sees first-time marathon runners walk through his door is right around the 17-mile mark. It's a telling pattern.
By that stage, the cumulative stress on tendons, joints, and connective tissue has been building for weeks, and for many runners it's the point where the body finally says enough, if it hasn't been listened to. If you're approaching that territory and something doesn't feel right, don't wait and hope it resolves itself. Book in early, before a niggle becomes a proper injury that derails months of work.
I have a monthly sports massage throughout my training to work through any tightness, keep the legs feeling fresh, and catch anything building before it becomes a problem, it's one of the best investments you can make in a training block. Sleep, nutrition, not rushing your mileage build, and proactive body maintenance are what get you to the start line healthy.
Glycogen depletion becomes a real factor in long runs above 90 minutes. Your body stores roughly 90 minutes of glycogen at moderate effort. Beyond that, you're relying on fat as fuel, which is slower to access, and on whatever carbohydrates you take in during the run. This is why fuelling during training matters, and why practising your race-day nutrition strategy on long runs is non-negotiable.
Fuelling and Nutrition: You Cannot Ignore This
Marathon nutrition is not an afterthought. Get it wrong and the race becomes an exercise in survival. Get it right and you'll cross the line feeling like you genuinely ran it, not just endured it.
Daily Nutrition in Training
As your weekly mileage increases, so does your energy requirement. Many first-time marathon runners under eat, which leads to fatigue, poor recovery, and increased injury risk.
Carbohydrates are your primary training fuel. Don't fear them. Rice, pasta, bread, oats, potatoes, these are your friends during a marathon build. Focus on timing: a carbohydrate-rich meal 2–3 hours before a long run, and carbohydrate-protein recovery nutrition within 30–45 minutes of finishing.
Protein is critical for muscle repair and adaptation. Aim for a serve of protein at every main meal, eggs, fish, chicken, legumes, Greek yogurt. Runners consistently underestimate how much they need, especially during heavy training weeks.
Hydration is ongoing, not just around runs. Increase your daily water intake, watch for signs of dehydration (dark urine, persistent headaches, unusual fatigue), and include electrolytes, particularly sodium, during longer sessions.
Iron is worth monitoring, particularly for female runners and those who've recently increased mileage significantly. Fatigue that persists despite adequate sleep and food can sometimes be iron deficiency. A blood test is the only way to know.
Fuelling During Long Runs
The general guideline is to take on 60–90g of carbohydrates per hour for runs over 90 minutes. That might be gels, chews, real food (dates and bananas work well), or a combination. Whatever you plan to use on race day, you must practise with it in training. The gut needs time to adapt to taking on food while running, and race day is not the time to discover that a particular gel doesn't agree with you.
Start fuelling earlier than you think you need to, around 15–20 minutes into a long run. Don't wait until you feel empty; by then you're already behind.
What I Actually Use: Tried and Tested Products
After years of running ultras and long endurance events, I've tried a lot of products and landed on a small set that I trust completely. For anyone starting out, the noise around sports nutrition can be overwhelming, so here's what works for me, for what it's worth.
For hydration and electrolyte replacement, my go-to is the Precision Fuel & Hydration PH series — electrolyte tablets that dissolve directly in your water bottle. The range covers PH 500, PH 1000, and PH 1500, with the number reflecting milligrams of sodium per litre — moderate, strong, and very strong respectively — designed to match different sweat rates and conditions. If you're not sure which you need, Precision offer a free online Sweat Test on their website that takes the guesswork out of it entirely.
Getting your electrolyte balance right, particularly sodium, is one of the most underrated aspects of marathon fuelling, and these tablets make it very straightforward to manage. Importantly, the tablets are low calorie, meaning they handle hydration without interfering with your carbohydrate strategy.
For gels, I use Precision exclusively, the PF 30 and PF 90. Both use a 2:1 glucose to fructose ratio, which allows the body to absorb carbohydrates more efficiently than single-source gels. What I appreciate most is the mild, neutral taste, after three or four hours of running, heavily flavoured gels can become genuinely unpleasant, and the PF range avoids that entirely. They're also notably easy on the stomach, which matters a great deal during long efforts when the gut is under stress.
The PF 90, affectionately known as the "Jumbo Gel", is a resealable 153g pouch containing 90g of carbohydrates, essentially three PF 30 gels in one. It's straightforward to carry in a vest pocket and easy to take in stages across a long run without the faff of managing multiple wrappers. One important note: the PF gels contain no electrolytes by design, they're intended to pair with the PH hydration range, so you're managing carbs and electrolytes independently and precisely.
I also use Infinit :GO FAR drink mix, particularly on longer efforts where I want to simplify my fuelling strategy. :GO FAR is an all-in-one isotonic powder that dissolves in water and delivers a full electrolyte blend, sea salt, potassium, magnesium, and calcium, alongside carbohydrates and a small amount of protein to help curb hunger and keep blood sugar steady during extended efforts. It uses three different carbohydrate sources (maltodextrin, glucose, and sucrose), which the body can process more efficiently than a single carb source.
On very long runs and ultras, reducing the number of things you need to think about and carry is genuinely valuable, with :GO FAR in the bottle, hydration and a significant portion of my carbohydrate target are covered in one drink. It's specifically designed for efforts of three hours or more, which makes it well suited to marathon long runs and race day itself.
Across all of this, my target is 60–90g of carbohydrates per hour, adjusted upward for longer runs, higher intensity, and warmer conditions. That range sits at the higher end of common guidance, but it's what my gut has adapted to through consistent training, and it's what keeps me moving well in the later miles.
For a first marathon, starting at 45–60g per hour and building from there is a sensible approach, give your gut time to adapt to in-run fuelling just as you give your legs time to adapt to the distance.
The Mental Game: The Real Marathon Starts at Mile 20
Physical preparation gets most of the attention in marathon training, but ask anyone who's run one what the real challenge is and they'll tell you: it's the head.
Miles 18–22 are where first-time marathon runners most commonly encounter the wall, that point where glycogen is depleted, legs have been running for over three hours, and the mind starts negotiating hard. The inner voice that asks whether it's really worth it, whether you could just walk, whether stopping would actually be so bad.
Here's what I know from hundreds of miles of endurance running: that voice lies. It's your body's protective mechanism kicking in, not a reliable signal that you can't continue. Learning to distinguish between "this is hard and I need to slow down slightly" and "I genuinely need to stop" is one of the real skills of distance running.
A few things that help:
Know your why. Why did you sign up for this? Write it down. When the miles get hard, your reason for running matters more than your training mileage. Running gave me purpose after my cancer diagnosis in 2021, knowing why I run has carried me through my darkest miles and my hardest days. Your why doesn't need to be dramatic to be powerful. It just needs to be real.
Break it down. Don't think about 26 miles when you're at mile 22. Think about the next lamppost. The next aid station. The next kilometre. Distance running is just a long series of small decisions to keep going.
Prepare for the dark patches. They will come. In training, in the race, sometimes both. Knowing they're coming means you're not shocked when they arrive. Every runner at every level has them.
Celebrate your training. Every completed long run is proof that your body is adapting. Every week you stick to the plan is progress. Don't wait for race day to feel proud.
Check out my article on the mental aspect of running - Race day Doubt - The Mental Game
Managing Training Fatigue: The Art of Listening to Your Body
Training fatigue is not the enemy, unmanaged fatigue is. There's a difference between the productive tiredness that follows a hard week of training and the kind of fatigue that's telling you something is wrong.
Signs you need more rest: persistent heavy legs that don't ease up even after easy days, disrupted sleep, elevated resting heart rate, declining motivation, irritability, getting sick more often than usual, pain that worsens during or after runs rather than easing.
Signs of normal training fatigue: tired legs on Monday after a Sunday long run, occasional low-energy runs, feeling worked at the end of a hard week.
The response to the first list is rest, a genuine rest day, or even a couple. Not a "light 5-miler." Rest. The body does not get stronger during training; it gets stronger during recovery from training. That distinction matters enormously.
Planned rest days are not a sign of weakness. In ultra running, knowing when to stop is as important a skill as knowing how to keep going. The same is true in marathon training. The runners I've seen get to start lines healthy and prepared are almost always the ones who were honest with themselves on the days their body said stop.
If pain is sharp, localised, and worsens with running, stop. See a physio before it becomes a proper injury.
Practical Tips for the Training Block
Get fitted for running shoes. Go to a specialist running shop and get properly assessed. The right shoe for your gait and foot type matters over marathon distances in a way it simply doesn't over shorter ones.
Rotate footwear. Having two pairs of trainers and alternating them extends shoe life and subtly varies the stress on your feet and legs.
Strength training. Two sessions a week of targeted strength work, single-leg exercises, glute activation, hip strengthening, calf raises, dramatically reduces injury risk and improves running economy. You don't need a gym or heavy weights. Head to YouTube for some excellent guides on running strength training.
Sleep. Underrated, underused, and free. Eight hours during heavy training weeks is not excessive; it's optimal. This is when your body repairs and adapts.
Run with others when you can. The running community is one of the most genuinely supportive communities I've encountered anywhere. Parkrun, local clubs, running groups, having people around you makes the miles easier and the experience richer.
Structured Training: Having a Plan That Adapts to You
One thing I'm often asked is how to structure a training plan that actually fits around real life, work, family, fatigue, the unexpected. Generic plans from the internet are useful but they don't know whether you had a terrible week, whether you're nursing a tight calf, or whether a big social commitment means your long run needs to move.
This is where having a genuinely personalised coaching tool makes a real difference, and it's why I've been using Runna, now part of Strava, as part of my own training. Runna builds a training plan around your specific goals, your current fitness, your available days, and adjusts as you go. Sessions are delivered directly to your GPS watch with pace targets and real-time audio guidance, and after every run you get a detailed breakdown of what you did and how it went.
For a first-time marathon runner in particular, that structure and personalisation takes away a lot of the guesswork and removes the risk of either training too hard or undershooting what your body can handle.
I'm a Runna ambassador, and through that I'm able to offer an exclusive two-week free trial, which is double the length of the standard trial and gives you full access to the premium app. That's enough time to set up a completely personalised training programme and run two full weeks of sessions before committing to anything.
If you're curious, you can download the app and enter code ANDY2 or redeem directly at web.runna.com/redeem?code=ANDY2
Race Day: A Few Final Thoughts
By the time you reach the start line, the training is done. Race day is about executing what you've practised.
Start slower than you feel like you should. The first few miles will feel easy, the crowd, the adrenaline, the taper freshness. Resist the temptation to bank time early. The marathon will always take it back.
Fuel as practised, not by how you feel in the moment.
If you hit the wall, slow down, not stop. Take a gel, walk a minute if you need to, talk to yourself firmly and kindly. You've done the training. The miles are in your legs.
And when you cross that finish line? That feeling, the exhaustion, the pride, the slight disbelief that you just ran 26.2 miles, belongs entirely to you. No one can train those miles for you. You ran them.
That's what makes the marathon worth every hard morning, every long run, every moment you wanted to stop but didn't.
See you at the finish.
— Andy Hood | Ultra & Endurance Runner | runningwestwardho.co.uk
Frequently Asked Questions: Training for Your First Marathon
How long does it take to train for a first marathon?
Most first-time marathon runners need 16 to 20 weeks of structured training, assuming they already have a reasonable running base, comfortably running 3–4 times per week with some runs of 30–45 minutes. Complete beginners who are new to running should allow additional time (often 3–6 months) to build that base before a dedicated marathon plan begins. Rushing the preparation is one of the most common causes of injury and burnout.
How many miles a week should I run when training for a marathon?
This varies by fitness level, but most first-time marathon training plans peak at somewhere between 35 and 50 miles per week. The key is gradual progression, never increasing weekly mileage by more than 10% from one week to the next, with regular step-back weeks every third or fourth week to allow the body to recover and adapt. Consistency over months matters far more than any single big week.
Can a complete beginner run a marathon?
Yes, but it requires a realistic timeline and genuine commitment to building fitness progressively. A complete beginner should not jump straight into a 16-week marathon plan. Instead, spend several months first building a consistent running habit, programmes like Couch to 5K are an excellent starting point, and only then transition into marathon-specific training. With the right approach and enough time, a beginner absolutely can cross a marathon finish line.
What is the 10% rule in marathon training?
The 10% rule states that you should never increase your total weekly mileage, or your training effort, by more than 10% compared to the previous week. It exists because the cardiovascular system adapts to running relatively quickly, while muscles, tendons, and bones take significantly longer. That mismatch is where injuries occur. The rule acts as a safeguard, ensuring the body has time to catch up with the demands being placed on it.
What should I eat when training for a marathon?
Carbohydrates are your primary fuel during marathon training and should make up a significant part of your diet, oats, rice, pasta, potatoes, and bread are all excellent sources. Protein is equally important for muscle repair and recovery; aim for a serve at every main meal. Increase your overall food intake as weekly mileage rises, as many runners undereat during heavy training blocks and suffer fatigue and slower recovery as a result. Hydration and electrolyte intake also need to increase alongside your training volume.
When should I start fuelling during a long run?
Start taking on carbohydrates around 15–30 minutes into any run lasting longer than 90 minutes. Don't wait until you feel depleted, by that point you're already behind. Aim for 30–60 grams of carbohydrates per hour through gels, chews, or real food like dates or bananas. Crucially, always practise your race-day fuelling strategy during training runs. The gut needs time to adapt to taking on food while running, and discovering a gel doesn't agree with you on race day is a situation best avoided.
What is hitting the wall in a marathon and how do I avoid it?
Hitting the wall, sometimes called "bonking", typically occurs between miles 18 and 22, when the body's glycogen stores become depleted and energy levels crash sharply. It manifests as sudden, heavy fatigue, mental fogginess, and a strong urge to stop. You can reduce the risk significantly by pacing conservatively in the first half of the race, fuelling consistently from around 15 - 30 minutes in, and training your body to use fat as fuel through long, steady runs at easy effort. Good taper nutrition in the final days before the race also helps maximise glycogen stores.
How do I know if I'm overtraining?
Warning signs of overtraining include persistent heavy legs that don't recover between sessions, elevated resting heart rate, disrupted sleep, declining performance despite continued training, increased frequency of illness, loss of motivation, and any pain that worsens during or after runs. If several of these appear together, the right response is genuine rest, not a lighter run. The body adapts and gets stronger during recovery, not during the training itself. Listening to these signals early prevents them from escalating into injury or illness.
Is it normal to feel tired during marathon training?
Yes, cumulative fatigue is a normal and expected part of marathon training, particularly as weekly mileage builds. The key is distinguishing between productive tiredness, feeling worked after a hard week, needing an early night, legs that recover after a rest day, and the deeper fatigue that signals overtraining or illness. Scheduled rest days and step-back weeks are built into training plans for exactly this reason. Sleep, nutrition, and not rushing mileage increases are the best tools for managing training fatigue effectively.
How important is the mental side of marathon training?
Enormously important, and often underestimated. The physical preparation gets most of the attention, but the ability to manage discomfort, push through difficult patches, and stay present when everything is telling you to stop is what actually gets most people to the finish line. Knowing your reason for running, practising positive self-talk, and preparing mentally for the hard patches, rather than being shocked when they arrive, makes a genuine difference. Miles 18 to 22 are not primarily a physical challenge. They are a mental one.
What is the difference between training for a half marathon and a marathon?
The structural differences are significant beyond the obvious increase in distance. Marathon training involves more weekly mileage, longer long runs (typically peaking at 18–22 miles versus 12–14 for a half), and a much greater emphasis on fuelling during runs. The final third of a marathon, roughly beyond mile 18, tests the body in ways that half marathon training does not prepare you for. Specific long runs, practised nutrition strategies, and additional recovery weeks are all essential additions when stepping up from the half to the full distance.
How do I choose a marathon training plan?
The best training plan is one that fits your current fitness level, available time, and running history, not the one used by a friend with different experience. A personalised approach, where the plan adapts to how you're actually responding to training, is more effective than a generic schedule. Key things to look for in any plan: gradual mileage progression, scheduled rest and step-back weeks, a mix of easy and harder sessions, and long runs that build progressively towards race distance. If the plan has you increasing mileage faster than 10% per week or never scheduling rest, treat it with caution.
Andy Hood is an ultra and endurance runner based in North Devon. Following a cancer diagnosis and treatment in 2021, Andy has gone on to complete multiple ultra-marathons including a 170-mile run to Land's End on the South West Coast Path and two completions of the 160KM Tour du Mont Blanc. He writes about running, endurance, and the mental and physical challenges of going long at runningwestwardho.co.uk.
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