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If (Yasso) 800s can predict your marathon time, can 400s work for the half?


Many runners are aware of the now infamous Yasso 800s workout in which multiple 800m repeats are run with equal rest. In theory, the average time it takes to run the intervals can help predict your marathon time.

RELATED: Weekly Workout: Predict your marathon time with infamous Yasso 800s

So logically, if 800m repeats can predict a marathon time, shouldn’t 400m repeats be able to predict a half-marathon time?

The approach:

Just like with the Yasso 800s, start the workout with a very easy warm-up of 10-15 minutes that includes some strides (20-30 second accelerations) and running drills. A standard 400m track is an ideal place to run this workout as you’ll be running hard for one full lap.


When warmed up, run 8-16 x 400m repeats at the fastest pace you can sustain throughout the workout. The goal should be to run each repeat at the same pace. In terms of rest between intervals, you can either walk or do a slow jog for the same amount of time as you ran the last interval or simply do an easy lap (400m) between hard reps.

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Predicting time

The more repeats you run (12 is better than eight and 16 is better than 12), the more accurate the workout may be for predicting a potential half-marathon time. Once you’re done and cooled down, calculate the average time it took to run all the 400m repeats. This, in theory, should be the time you’re able to run a half-marathon. E.g. If you averaged 1 minute 30 seconds per lap, you should be able to run around 1 hour 30 minutes for the half.

Note: This is merely a useful and potentially predictive workout and by no means can we guarantee that this workout will accurately predict your half-marathon time. For some, speed comes naturally and this workout will provide an overly generous estimate of what you’re capable of. Others struggle with speed but can endure at longer distances and so may actually find this workout underestimates what they’re able to do. Regardless, you’ll need to be doing the appropriate amount and type of half marathon training–including longer intervals, tempo runs and long runs–if you want to be successful at the distance.

Got an upcoming half marathon? Try the workout then let us know how it goes.