How long should a marathon training plan be?

Sixteen to twenty weeks from a base of 20 to 25 miles a week. Twelve is workable if you already have the mileage. From no running at all, allow six months.

How many days a week should I run for a marathon?

Four is the practical minimum, five or six is better. Adding a fifth easy run is usually more valuable than lengthening the four you have.

What is the most important session in a marathon plan?

The long run, particularly once it starts carrying marathon-pace segments. If you can only protect one quality session a week, protect that one.

What happens if I miss a week?

Rejoin the plan where it is now rather than trying to catch up. One missed week costs almost nothing. Two hard weeks crammed into one costs a lot, sometimes the block.

Guide

How a marathon block is built

Every marathon plan you have seen is a variation on the same structure. Understanding the structure is more useful than following any particular plan, because it tells you what to protect when your sixteen weeks inevitably stop going to schedule.

The four phases

Sixteen to twenty weeks, in a sequence where each phase earns the right to the next.

1
Base, roughly weeks 1 to 5
Volume rises, intensity stays low. Long run from 10 to 14 miles. Strides twice a week and one light threshold session from week three. The job is aerobic capacity and tissue durability, and it feels like nothing is happening.
2
Build, roughly weeks 6 to 11
Two quality sessions a week: one threshold, one long run carrying marathon-pace segments. Mileage reaches its peak somewhere in here. Long run climbs to 16 to 18 miles. This is the phase that produces the fitness.
3
Peak, roughly weeks 12 to 14
The longest runs of the block and the most marathon-specific work. 18 to 20 miles with 10 to 14 at goal pace. Volume holds or dips slightly. The last long run lands about three weeks out.
4
Taper, weeks 15 to 16
Volume drops 40 to 60 percent across two to three weeks. Intensity is kept. Fatigue clears faster than fitness fades, and the gap between them is your race.

The weekly shape

Through the build phase, a typical week is five to six runs: two quality days and the rest easy. The two quality days are the threshold session and the long run, spaced at least three days apart.

Everything else is easy running, and it should be a clear majority of the weekly volume. In a 45 mile week with 40 minutes of threshold and 12 marathon-pace miles inside the long run, roughly 36 of the 45 miles are easy. That ratio is not a compromise; it is the design.

What to protect when the block goes wrong

It will. Here is the order of importance when you have to drop something.

Protect the long run first. It is the least replaceable session in the block. If you can only do one quality session in a week, do this one.
Protect the threshold session second. It is the main driver of your sustainable pace and it is cheap in recovery relative to what it gives.
Drop intervals first. The highest injury risk per unit of marathon-relevant fitness. In the last six weeks they are close to optional anyway.
Never make up missed volume. A missed week is gone. Rejoining the plan where it is now is correct; trying to run last week and this week in one is how a missed week becomes a missed block.

Frequently asked

How long should a marathon training plan be?: Sixteen to twenty weeks from a base of 20 to 25 miles a week. Twelve is workable if you already have the mileage. From no running at all, allow six months.
How many days a week should I run for a marathon?: Four is the practical minimum, five or six is better. Adding a fifth easy run is usually more valuable than lengthening the four you have.
What is the most important session in a marathon plan?: The long run, particularly once it starts carrying marathon-pace segments. If you can only protect one quality session a week, protect that one.
What happens if I miss a week?: Rejoin the plan where it is now rather than trying to catch up. One missed week costs almost nothing. Two hard weeks crammed into one costs a lot, sometimes the block.

Stop reading. Start training.

This is the theory. Shed is the schedule.

Knowing what a threshold run is for does not tell you which Tuesday to run one, or how fast, or what to do when you miss it. Shed writes every session of your race block and adjusts it as you train. Ask it where a number came from and it will tell you.

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