Built by Tommo, Verus founder — free to use, no account required.
Marathon Training Duration Calculator
Four starting points, one honest number of weeks.
Marathon Training Duration Calculator
Pick where you're starting from, and see how many weeks the block actually takes — and, with a race date, the week to start.
Where you're starting from
Training block
16-20 weeks
Base
6 weeks
Raise weekly volume and consistency. No heroics — this is where most of the injury risk in the whole block gets managed.
Build
9 weeks
The longest sessions, threshold work, and race-pace effort layered into them.
Peak
3 weeks
The hardest stretch of the block — the volume and intensity both near their maximum.
Taper
2 weeks
Volume drops sharply, intensity mostly stays. This is where the training becomes fitness.
General planning guidance based on well-established, mainstream training-week ranges — not a personalised coaching plan. Uses the longer end of the range for the phase breakdown and start date, since starting a little early costs a taper week and starting a little late costs the race.
Use It On A Real Race
About This Tool
"Sixteen weeks" is the popular answer because that's how long most published plans run — but it's only true for the runner already covering 15-20 miles a week. This calculator asks where you're actually starting from and gives the real range, from a standing start through to someone with a recent half marathon behind them, plus the week to begin if you already have a race date.
How To Use It
- Pick the description that matches where your running is right now.
- Add your race date if you have one, to get a start-by date.
- Read the weeks needed, and the base/build/peak/taper breakdown of what they're for.
- If the start date is already in the past, that's useful information — it means the next cluster of marathons, not a compressed plan.
"Sixteen weeks" is the popular answer because that's how long most published plans run. It's also only true for one specific runner — someone already covering 15-20 miles a week who can run a 10K. Everyone else is starting the clock from a different place, and the calculator above asks which one you actually are before giving you a number.
The four starting points
| Where you are now | Weeks to the start line | What the time is for |
|---|---|---|
| Not currently running | 39-52 weeks | Roughly six months building to a comfortable 10K and a consistent 20-mile week, then a full 16-20 week marathon block on top. |
| Running 30 minutes comfortably | 26-35 weeks | Two to three months raising weekly volume and getting a long run to 10 miles, then the 16-20 week block. |
| Running 15-20 miles/week, can run a 10K | 16-20 weeks | Straight into a marathon block. This is the runner every published plan is written for. |
| Running 30+ miles/week with a recent half marathon | 12-16 weeks | You already have the base. The block is about marathon-specific long runs and race-pace work. |
The honest test
Can you run for an hour, today, without stopping and without it being an event? If yes, you're ready to start a 16-week block. If no, the sixteen weeks starts after you can.
Why the number varies so much
Cardiovascular fitness improves in weeks. The structures that carry you — tendons, ligaments, bone, connective tissue — adapt over months. That mismatch is the single most common cause of marathon training going wrong: your engine outpaces your chassis, you feel great, you add volume to match how you feel, and something objects.
This is why the answer isn't a fitness question. Nearly everyone who fails to reach a marathon start line healthy did so by treating it as one.
What the weeks are actually for
Whatever your total comes to, it's built from the same four phases in roughly the same proportions — base to raise volume safely, build to add the long runs and race-pace work, peak as the hardest stretch, taper to let it become fitness. The calculator above breaks your own total into these four automatically.
Want the full picture?
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Frequently Asked Questions
How long does it take to train for a marathon from scratch?
Nine to twelve months if you're not currently running — roughly six months to build to a comfortable 10K and a consistent 20-mile week, then a full 16-20 week marathon block on top. The limit isn't fitness, which improves in weeks; it's tendon, bone and connective tissue, which adapt over months.
Is 16 weeks enough to train for a marathon?
Yes, if you can already run for about an hour without stopping and are covering 15-20 miles a week — that's the runner almost every published 16-week plan is written for. If you can't yet, the sixteen weeks starts after you can.
Can I train for a marathon in 12 weeks?
If you've run marathons before and kept running consistently through the year, yes — you never lost the base. Building from nothing in twelve weeks mostly raises the risk of injury or a walk after twenty miles. With a fixed date and a short runway, change the goal rather than the schedule.
How many hours a week is marathon training?
Four to six hours a week at peak to finish comfortably, six to eight to run a specific time, eight to ten or more to chase a personal best. The long run dominates all three and grows through the block — that's most of a weekend morning, most weekends, for four months.
What is the base, build, peak and taper structure?
Base raises weekly volume with no heroics. Build adds the longest long runs and marathon-pace work inside them. Peak is the hardest fortnight of the block. Taper drops volume 40-60% while keeping intensity — it's where the training actually becomes fitness, and cutting it is one of the more reliable ways to arrive tired.