How to predict your race time

When I was at personal trainer school one of the things we learned was to find somebody’s ‘one rep max’ (1RM) which is the maximum amount of weight they can lift one time.

It’s supposed to be a measure of absolute strength but in practice it’s utterly pointless.

Lifting as much weight as you can on a bench press or squat can be downright dangerous, and most of us will give out mentally way before we fail physically.

A much better way is to use a 10RM to predict your 1RM.

You find a weight you can lift only 10 times, and you can then predict what you’d be able to do just one time, without actually having to do it.

Similar tables and formulae exist for running, and I thought you might find it interesting to check out your ‘predicted stats’ for distances from 200m right up to 200km.

If you know your time for any distance, you can use it to predict your time for any other distance, which is useful information to have.

This tool from includes 4 different calculators

One thing that’s interesting is the variability between the results each of the calculators gives.

They all have slightly different formulae for predicting your time so it’s not an exact science, but it’s still useful information to have.

There also appears to be a problem at the extreme distances.

Just for fun I plugged in my old 400m PB and it predicted that I should be able to run a marathon in 1:56.

Not entirely sure I believe that ;)

It also gives me a 100 mile time of 8 hours, so the accuracy clearly falls away at the extremes.

The best (and most accurate) use of the calculators is for predicting between 5k and marathon.

If you’re training for an event it’s good to have a clear target to aim for.

By putting in a shorter distance race in the run up to the main event, you can use your results to predict roughly where you should be setting your sights.

This may end up being faster or slower than your original target.

Whilst you need to take the prediction with a pinch of salt, it can still be useful information to have for plotting your race day tactics.

We use this principle in all of my main training programs: in the iMarathon there’s a half marathon time trial, in the iHalf there’s a 10k, and in the i10 Project there’s a 5k.

(Interestingly, many runners doing these programs report personal best performances in their time trial races which is always a nice little bonus!)

Check out this calculator, and if you’re ever working with a personal trainer who tries to get you doing a 1RM on your first session, run a mile