How many weeks do I need to train for a marathon?

Sixteen to twenty from a base of 20 to 25 miles a week. From nothing, allow six months: three to build a base, then the block. Twelve-week plans exist and work for people who already have the mileage.

How many miles a week for a first marathon?

Peaking somewhere between 35 and 45 miles a week is normal and sufficient. You can finish on less. Below about 25 at peak, the last 10K becomes a survival problem rather than a running one.

Should I run 20 miles before the marathon?

One to three runs of 18 to 20 miles is the standard, with the last about three weeks out. If that takes you over three and a half hours, cap it at time instead. Nobody has ever failed a marathon because their longest run was 18 rather than 20.

How long should I taper?

Two to three weeks. Volume comes down, intensity stays in. Cutting the hard sessions entirely is the common error and it leaves you flat on the day.

Train for

Training for your first marathon

The marathon is the first distance where being fit is not enough. You have to arrive healthy, and most people who fail a first marathon do not fail on race day. They fail in week nine, doing too much, too soon, too fast.

Where you need to be before you start

A marathon block builds on a base. It does not create one. Before week one you want:

Consistency. Three to four runs a week for at least the last two months, without gaps you had to recover from.
A base of 20 to 25 miles a week. Roughly 32 to 40km. If you are at 12, spend six weeks getting to 20 before the block starts. That is not lost time, it is the foundation the block stands on.
A long run of 8 to 10 miles. You should already be able to run this without it wrecking your week.
No live injuries. Something that hurts now will hurt more at 40 miles a week. Deal with it first.

How the sixteen weeks are shaped

A first marathon block is usually 16 to 20 weeks, in four phases. The phases are not decoration. Each one earns the right to the next.

1
Base, weeks 1 to 5
Volume climbs, almost all of it easy. The long run moves from 10 to 13 miles. One session a week gets a bit of structure, usually strides or a short tempo. The job here is durability, not speed.
2
Build, weeks 6 to 11
The long run grows toward 18 miles and starts carrying marathon-pace segments. One quality session a week becomes two: usually a threshold run and marathon-pace work inside the long run. Weekly mileage peaks somewhere between 35 and 45.
3
Peak, weeks 12 to 14
The two or three longest runs of the block, 18 to 20 miles, with the last one about three weeks out. This is where a first marathon is won, and it is also where it is most often lost by pushing to 22 or 24 because the internet said so.
4
Taper, weeks 15 to 16
Volume drops by roughly a quarter, then by half. Intensity stays. You will feel sluggish and slightly mad. That is the taper working, not failing.

How far the long run should actually go

Twenty miles is the conventional ceiling for a first marathon, and there is a good reason it is not 26. The cost of a long run rises steeply past about three hours: the recovery it demands starts eating the quality sessions that follow it, and the injury risk climbs faster than the fitness does.

For most first-timers the honest ceiling is time, not distance. If 20 miles is going to take you three and a half hours, run three hours and stop. You get almost all of the adaptation and considerably less of the damage. The last six miles of the marathon are run on fitness built across the whole block, not on having rehearsed them.

The three mistakes that end first marathons

Easy runs run too hard. This is the big one. If most of your week is moderately hard rather than genuinely easy, you accumulate fatigue without the adaptation that hard training is supposed to buy. Easy should feel almost embarrassing. Conversational, nose-breathing, a pace you could hold all day.
Chasing the long run. Adding a mile every week because last week felt fine. The long run should step up, then step back, then step up further. Three weeks forward, one week down.
Ignoring the first twinge. Almost every marathon injury announced itself two weeks earlier as something minor that got run through. Three easy days now costs you nothing. Three weeks off in week twelve costs you the race.

What to run on the day

Your first marathon goal should be to finish strong, not to hit a number. Pick a pace you are confident you can hold, then run the first 10K slower than that.

The most reliable first-marathon strategy is the least exciting one: run the first half feeling like you are holding back, take fuel every 30 to 40 minutes from the start rather than when you need it, and let the race come to you after 20 miles. Everyone who blows up in a first marathon did something at mile 6 that felt easy at the time.

Frequently asked

How many weeks do I need to train for a marathon?: Sixteen to twenty from a base of 20 to 25 miles a week. From nothing, allow six months: three to build a base, then the block. Twelve-week plans exist and work for people who already have the mileage.
How many miles a week for a first marathon?: Peaking somewhere between 35 and 45 miles a week is normal and sufficient. You can finish on less. Below about 25 at peak, the last 10K becomes a survival problem rather than a running one.
Should I run 20 miles before the marathon?: One to three runs of 18 to 20 miles is the standard, with the last about three weeks out. If that takes you over three and a half hours, cap it at time instead. Nobody has ever failed a marathon because their longest run was 18 rather than 20.
How long should I taper?: Two to three weeks. Volume comes down, intensity stays in. Cutting the hard sessions entirely is the common error and it leaves you flat on the day.

Your block, written

Put a date on it and Shed builds the weeks.

Shed takes your goal, your race date, and the days you can actually run, then writes every session between here and the start line. It reads each run off your Apple Watch the same day and moves what needs moving. No spreadsheet, no guessing at paces.

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