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Training for your first marathon is one of the most physically and mentally demanding things most people will do. It takes 16–20 weeks of consistent training, requires managing injury risk carefully, and demands a level of commitment that changes how you organise your week for several months.
It’s also one of the most rewarding things you’ll ever do. This guide covers what a first marathon training programme looks like, what to expect as training progresses, and how to avoid the mistakes that derail first-timers.
Before You Start
You should be running regularly before you begin. Most marathon training plans assume you can run 3–4 times per week and cover 20–30 miles comfortably before starting the plan. If you’re starting from scratch, do a 5K training programme first, then a 10K and half marathon, before committing to marathon training.
If you can comfortably run for an hour at an easy pace, you have sufficient base fitness to start a marathon training plan.
How Long Training Takes
16 weeks is the minimum sensible preparation time for a first marathon. 20 weeks is better — it allows more gradual mileage build-up, reducing injury risk. Plans that promise marathon readiness in 12 weeks are pushing the boundary of what’s safe for most first-timers.
The bulk of the training (the long run) builds your aerobic base and trains your body to use fat as a fuel source alongside glycogen — a process that takes months, not weeks.
The Structure of a Marathon Training Week
A typical first marathon training week includes:
- One long run (the centrepiece of the week)
- Two or three easy runs (at a genuinely easy, conversational pace)
- One quality session (optional for first-timers — tempo run or intervals)
- 1–2 rest days (essential — adaptation happens during recovery)
- Cross-training option (cycling, swimming — low-impact aerobic work)
The mistake most first-timers make is running all their runs too hard. 80% of your weekly running should be at an easy, conversational pace — one where you could hold a full conversation without gasping.
The Long Run
The long run is the most important session in marathon training. Each week, it extends slightly:
- Weeks 1–4: 10–14 miles
- Weeks 5–8: 14–18 miles
- Weeks 9–12: 18–20 miles (peak weeks)
- Weeks 13–16: Taper (mileage drops as race day approaches)
The long run should be slow — approximately 60–90 seconds per mile slower than your goal marathon pace. The purpose is aerobic conditioning and fat-burning adaptation, not speed.
Fuel during long runs: Once your long run exceeds 1.5 hours, you need to fuel during the run — typically 30–60g of carbohydrate per hour (energy gels, chews, or sports drinks). Practice this during training, not for the first time on race day.
The Taper
The 3-week taper before the race is where most first-timers make a second mistake: maintaining high mileage too close to the race, arriving at the start line fatigued.
The taper reduces weekly mileage by approximately:
– Week 3 before race: 70–80% of peak mileage
– Week 2 before race: 50–60% of peak mileage
– Race week: 25–30% of peak mileage (mostly easy running until the race)
You will feel sluggish during the taper. This is normal and temporary — the body is storing glycogen and repairing tissue. Don’t be tempted to run more because you feel like you’re losing fitness.
Nutrition During Training
Carbohydrates are the primary fuel for marathon running. Restricting carbohydrates during marathon training is counterproductive — you need them to fuel long runs and to recover afterward.
Protein matters for recovery: 1.4–1.7g of protein per kg of bodyweight per day is appropriate for high-mileage training weeks.
Weight management during marathon training: Many first-timers expect to lose significant weight during marathon training. This often doesn’t happen — appetite increases with training load, and the body adapts. Weight loss, if it happens, is a secondary benefit, not the mechanism of marathon training.
Common First-Timer Mistakes
Running too fast on easy days: The easy runs should genuinely be easy — if you’re breathing hard, slow down. Running easy days too fast accumulates fatigue that prevents quality sessions and long runs from being effective.
Skipping the long run: The long run is the foundation. Missing several long runs because of weekend plans significantly compromises preparation.
Wearing new shoes on race day: All race-day gear — particularly shoes and socks — should be worn in training beforehand. New shoes on race day causes blisters.
Ignoring niggles: A minor shin pain that becomes a stress fracture, a tight IT band that becomes ITBS — most marathon-ending injuries have warning signs that are ignored. Take rest days seriously.
Going out too fast on race day: The most common first marathon mistake. The adrenaline, the crowd, the excitement — all push you to run faster than your training pace in the first miles. The second half of a marathon is brutal if you do this. Start at your planned pace regardless of how good you feel.
What a Realistic First Marathon Time Looks Like
First marathon times vary enormously. A very broad guide:
| Prior running background | Realistic first marathon time |
|---|---|
| Occasional 5K runner | 5–6 hours |
| Regular half marathon runner | 4–5 hours |
| Sub-2 hour half marathon | 4–4.5 hours |
| Sub-1:50 half marathon | Under 4 hours |
The goal for a first marathon is finishing, not time. Pick a pace that feels comfortable in training and stick to it.
Summary
Marathon training rewards patience, consistency, and restraint:
- Start with at least 20 miles/week of comfortable running before beginning a marathon plan
- Run your easy days at an easy pace — conversational effort, regardless of how easy it feels
- Protect the long run above everything else in your weekly schedule
- Fuel during long runs over 1.5 hours — practice with gels in training, not for the first time on race day
- Start the race slower than you think you should — the back half of a marathon punishes early enthusiasm
Next read: Running a half marathon for the first time: what to expect