Shed

Free tool · Yasso

Yasso 800 Calculator

Enter your average across 10 x 800m and see what the Yasso rule of thumb says your marathon is worth, alongside what a physiological model says. Where the two disagree is the interesting part.

Yasso says

3:10:00

About 7:15/mi for 26.2 miles.

A second opinion

  • Yasso prediction

    The rule of thumb: 3:10 per 800 means a 3:10 marathon

    3:10:00

  • VDOT prediction

    Treating the 800 average as a race effort and modelling forward

    3:40:26

  • Implied VDOT

    From the 800m average

    42.0

Reading the gap

The physiological model says slower than Yasso does. That is the normal pattern: Yasso flatters runners with good leg speed, and the marathon is decided by mileage the 800s cannot see.

Neither number knows your weekly mileage, and that is what actually decides a marathon. Treat both as a sanity check on a goal you set from your training, not as a prediction.

Stop calculating. Start training.

These numbers are the first 30 seconds of what Shed does.

Shed reads your Apple Health, grounds your VDOT in your actual training — not one race — and writes the whole block: every workout, every pace, adjusted as life happens. The calculator gives you a snapshot; Shed gives you the plan.

Get your plan on iPhone

The workout

Ten repetitions of 800 metres, with a jog recovery equal in time to the rep. If you run 3:10 for the 800, you jog 3:10 before the next one. Run them evenly: the point is a repeatable average, not a fast first rep and a survival exercise from rep six.

It is a genuinely useful session regardless of the prediction. Ten by 800 with equal recovery is a substantial aerobic workout at roughly 5K to 10K effort, and building toward the full version over a block is a reasonable way to structure interval training.

Why it flatters some runners

The marathon is decided by aerobic durability, which is built with weekly mileage over months. A set of 800s measures something related but different: your speed and your ability to repeat it with recovery.

A runner with a 19 minute 5K and 25 miles a week can hit 3:05 averages and run 3:35 for the marathon. Nothing in the workout can see the mileage, so nothing in the prediction accounts for it. Use it as one input among several and set your goal from your training.

Frequently asked

What are Yasso 800s?
A workout and a rule of thumb from Bart Yasso, longtime race director at Runner’s World. You run 10 x 800 metres with a jog recovery equal to the rep time, and your average, read as minutes and seconds, is said to predict your marathon in hours and minutes. A 3:10 average suggests a 3:10 marathon.
Do Yasso 800s actually work?
Sometimes, for a particular kind of runner. It works reasonably well for people whose speed and endurance are balanced. It flatters runners with good leg speed and thin mileage, which is unfortunately the group most attracted to a workout that promises a marathon prediction from a track session.
How much recovery between reps?
Equal to the rep. If you run 3:10, jog 3:10. Shortening the recovery makes the workout harder and the prediction meaningless, and lengthening it does the opposite.
When should I do the workout?
Build toward the full 10 reps over several weeks, and do the complete version somewhere around three to five weeks before the marathon. It is a hard session in its own right and needs a proper recovery day after it.
Is it better than a VDOT prediction?
No, and it is not really trying to be. VDOT models physiology consistently across distances. Yasso is a heuristic that happens to work often enough to be memorable. Where they disagree, the gap tells you something about whether your speed or your endurance is ahead.

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