Can you estimate your marathon time based on your 10K PB?

Whether you’re a marathon newbie or seasoned pro, it can be difficult to accurately estimate your likely time for running 26.2 miles.

Some people like to base it off a half-marathon PB, multiplying it by two and adding somewhere between 10 and 15 minutes. But there’s another method, favoured by some coaches, based on your 10K time.

The formula is this: 5 x 10K time, minus 10 minutes. Of course, there are some caveats: the 10K time has to have been achieved in the same training cycle and have been run at race-day effort.

It’s a formula first suggested by legendary British running coach, and founder of the British Milers Club, Frank Horwill in his book How far is your longest marathon training run. columnist and national endurance manager for England Athletics, believes it has plenty of merit, RW Published: 13 March 2024.

‘I have always found it to be a useful guide and it gives a pretty good ball park goal,’ he said. ‘A helpful way for athletes to think of it is, if you can start your specific marathon training in great 10K shape, you have an excellent starting point. Of course for runners to realise the goal they need to train specifically for the demands of the marathon, but it gives an useful reference point.’

Does this workout predict your half-marathon time Jo Wilkinson isn’t quite as sold on the formula. ‘Any race distance can be used to predict marathon times, but accuracy is likely to be improved the closer the race distance is to the marathon,’ she said. ‘So half-marathon time is likely to be better to predict marathon times than 10K. However, this formula gives you a good indication of potential marathon time based on 10K.’

Wilkinson adds that the best predictor for marathon time also takes into account the volume and breakdown of the training that you do for the marathon. ‘The greater the consistent volume of training, the better you are likely to run on the day,’ she said. ‘Then there are important factors such as good pace judgement and good race nutrition that has been practised in advance. For the marathon, more so than any other endurance event, poor pacing and poor race nutrition can have a hugely detrimental impact on your finishing time.’

If you’re interested in trying to estimate your marathon time based on your 10K PB, take a look at the below table to see where you sit.