RW's Race Time Predictor

Predict your race result - just enter a recent time from another distance

RW Race Time Predictor

This calculator lets you input an actual race time to see what you should be capable of at another distance. It is adjusted for distance (ie its 10K prediction isn't just double your 5K time), but there are three caveats:

  1. It assumes you've done appropriate training for the distance. Doing a 22-minute 5K today doesn't mean you can do a sub-4 marathon tomorrow. Obvious, really.
  2. It assumes you don't have a natural significant bias towards either speed or endurance. Some people, no matter how much training they do, will always over-achieve at one end of the scale.
  3. The calculations become less accurate for times under three and a half minutes and over four hours.

Recent race length (you can use a decimal point, eg. 26.2):
My time (hours:minutes:seconds): : :
Please estimate my time for:
Predicted time (hours:minutes:seconds): : :

The formula was originally devised by Pete Riegel, a research engineer and marathoner, and published in Runner's World many moons ago by Owen Anderson in 1997. It has stood the test of time since then and has been widely used.

The formula is T2 = T1 x (D2/D1)1.06 where T1 is the given time, D1 is the given distance, D2 is the distance to predict a time for, and T2 is the calculated time for D2.

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predictor, 10km, half marathon, marathon, race time, raceday goal, raceday misc, marathon goal, pace

Discuss this article

Hello all

we'd love to know whether this calculator (click the link above) matches your real-life race times.

It's based on a well-established formula - what do you think?

My first reaction was that its predictions were too fast, but I think that was because
a) I have a bit more speed than endurance; and
b) my instinct was to try to predict times at the extreme ends of the distance spectrum (eg marathon time from 5K time)

Sean, RW

Posted: 23/11/2004 at 13:39

Well, it thinks that I should be about a minute faster over 10k than I've ever run. That's probably about right though as I'm better trained for endurance and prefer racing longer distances.

I very much hope it's accurate, because it's tipping me for a 2:53 marathon ;o)
Posted: 23/11/2004 at 13:52

Seems pretty accurate for me, but my 10k time is quite slow for my marathon time compared to a lot of other people's.
Posted: 23/11/2004 at 13:56

It thinks I should be slower over 10K than I actually am. This is based on 10 mile and half times.

About a minute out from my PB of 36:58, based on a 10 mile time of 1:02:43.
Posted: 23/11/2004 at 14:24

I think it works pretty well - my 10K PB predicts a half-marathon time less than a minute quicker than my actual best half. Frustratingly, the two half-marathon times are either side of my goal of 1:45! So, there's hope!

I have a copy of this formula in my running log to give me an idea of how easy or hard a run really was - every run is converted to a predicted time for a half-marathon so that I have a standard to measure against.
Posted: 23/11/2004 at 14:43

My 10m time would predict a sub 2:40 marathon, though reality is different, 12 minutes behind. Based on shorter distances, I ran faster times than predicted.
Posted: 23/11/2004 at 14:44

It's great news for me because my 10k PB of 42:28 predicts my marathon time as being 3:15:09 and as I'm going for sub 3.15 in 5 months time, it's an indication that providing I get the training is, I should achieve it without too much difficulty...
Posted: 23/11/2004 at 15:09

Works within parameters give or take a couple of minutes on the marathon time
Posted: 23/11/2004 at 15:27

I suppose that what it doesn't take into effect is that each race is different. So its an indication only. That's unless your running around a track.
Posted: 23/11/2004 at 15:27

Also if you use it to predict 10K from a 400M time then its waaaaay off.
Posted: 23/11/2004 at 15:29

yes, the formula was found to work best for 3.5 mins to 4hrs - (or 230 mins to be precise). I think it mentions that on the page
Posted: 23/11/2004 at 15:45

aaah I never read instructions!
Posted: 23/11/2004 at 15:47

URR, I knew you were in 2:40 shape:)

Well according to my recent marathon I'm in 35:17 10k shape - let's see if we can take a couple of secs off that on Sunday;)

My 10k pb predicts a sub 2:35 marathon - lol!!
Posted: 23/11/2004 at 15:52

Just input a recent run I did for 13.1 miles, not a race but just ran a bit faster than normal, RW predicts a 4.48.49 marathon time yet the mcmillan predicts 4.52.10, about 3 and half mins difference!! My marathon PB is actually 5.11.

Both times do fit in with my aim to do 11 min miling for my next marathon.
Posted: 23/11/2004 at 15:58

the only time i could put in as an official time is a ten miler this predicts a 10k time of just over 52 mins i need to do a 10k to see if i could do it a bit quicker than that hopefully
Posted: 23/11/2004 at 16:01

It's accurate to one second for 10K/half, but not really for marathon.

A 2:53 marathon from a 37:42 10K seems a bit aggressive.

Posted: 23/11/2004 at 16:30

It's pretty accurate although it seems I've still got a bit more room for improvement over the longer distances going by my 5k time. It predicts a marathon of 3:12:16, something to work at then for FLM:o)
Posted: 23/11/2004 at 17:42

Sean, check out my post on the 2:30 thread here

which I did a few days ago. It shoes how to test the relationship between your times. For my 5k, 10k, 10M and HM times the relationship is Riegel's exactly but with 1.0508 instead of 1.06. The r-squared value of the relationship for my pbs is 1 which is the real proof in Riegel's hypothesis when applied to me.
Posted: 23/11/2004 at 17:55

Nice stuff, Mike. Do you mind if I lift that into a 'find out more' page?

Have you seen this race-time ranking calculator on RW US? It's a hidden link that has now been replaced by 'under construction' message on the front of their site, so I'm not sure what's going on there.

That's another one to adapt for the UK
Posted: 23/11/2004 at 18:27

Mine get steadily worse the longer I run. Maybe I haven't done a flat marathon or half yet to compare though.

Posted: 23/11/2004 at 19:20

doesn't work for me

my half marathon "should" be faster than my PB even if I enter my PW 10k time

Posted: 23/11/2004 at 19:24

seems about right for me, using my known training run times (not raced properly yet).

Rather interesting to see that should I ever do a complete U-turn and actually try a marathon, that I'd be on for five hours, when I thought it would be much nearer six...
Posted: 23/11/2004 at 19:26

I'll get back to you you on that
according to 10k time should take 30 seconds of 5k best (not run since sept) and 8 minutes of my half (last one was in June)
Posted: 23/11/2004 at 21:19

Almost spot on for all distances from 5k to half marathon, though it seems I am 5 mins too slow for 20 miles and 8 mins too slow for a marathon.

Personally I find that most race time predictors are too optimistic for the longer distance races.
Posted: 24/11/2004 at 12:51

Same for me - it works well for distances 5k to half marathon. But much as I would love to run the predicted 2-51 for a marathon, that's 10 minutes faster than I've actually managed.
Posted: 24/11/2004 at 13:38

I also found it quite accurate for distances 5k to 1/2m, however the marathon prediction calculates a time of 2 x 1/2m time + 6mins which I think is a bit optimistic. I've always thought that 2 x 1/2m time + 10mins is a good prediction of marathon potential.
Posted: 24/11/2004 at 13:54

The marathon time is faster than I've ever managed, too.

I wonder if most of us are just under-developed in terms of endurance (compared with speed). Certainly when Riegel first came up with the equation in the late 1970s, I guess the norm was towards training at much higher mileage than now.
Posted: 24/11/2004 at 15:15

I do suspect - without wishing to offend anyone - that most people d onot enough run enough miles to fulfil their marathon potential. I've always felt that training for any distance from 5k to 1/2m is pretty much the same, but marathon training is a completely different ball game.
Posted: 24/11/2004 at 15:34

Like the others it doesn't work for me.

Current form : 10k and HM in last 3 weeks - HM should have been 8 mins quicker

PB form in the Spring - HM should have been 5:30 quicker - 97 secs off that 90 min barrier, whereas in reality I'm a whole 7+ minutes away!
Posted: 24/11/2004 at 15:59

Surprisingly accurate for me, I'd say, Sean. I noticed the caveat is that you've done the adequate training and don't have any bias - well, I think I have a bias for shorter distances so I put in my Brighton time 44:58 and checked back to 5k. It gave me 21:34. A few days previous to Brighton I did 5k on the treadmill on 2% incline and got 21:19.

I've discovered that up to about 5k road is faster than TM on 2%, after that it goes the other way. 10k I have to add 1 min. I think it's something to do with the stride length?
Posted: 24/11/2004 at 16:13

It confirms to me how much I messed up my fist half training this year - gives me hope for a good chunk off next year (even if I don't hit the predicted fig) s'long as I can get my act together. :-)))
Posted: 24/11/2004 at 16:13

jenny, have you measured the speed of the treadmill at your 5k and 10k pace? I wonder if the speed is more accurate at one than the other? Though thinking about it, the lack of cooling effect/wind resistence on the treadmill should have different consequences at different speeds, so maybe that could account for it?

Posted: 24/11/2004 at 16:19

Foo Bar, no I haven't measured the speed, I've just taken the readings as correct. I think there is too little difference in speed for factors like lack of cooling (it's in the conservatory, windows and doors open plus fan!). I think it could be more to do with stride length. Faster speeds favour longer strides and it's much easier to do that outside. The treadmill automatically shortens your stride which would favour longer distances.

I'd be interested if someone else did this experiment - compare 5 and 10k times road to treadmill on 2%. Does RW have an opinion on this?
Posted: 24/11/2004 at 16:28

Don't suppose you've recorded your average heart rate for road versus treadmill 5k and 10k runs?

Posted: 24/11/2004 at 16:40

Using my 10k time as I've run a few (well 4) over a few years and they are all pretty close in time (within 7 seconds of each other).

My 5k time is about 10 seconds down on what it should be according to my 10k time, my half marathon time is 5 minutes 30 down on what it should be by my 10k time, my marathon predicted time is 2.52 ! - I've only run one which I did as a training run but I reckon about 3 hours is more realistic even when I was in form.

I do have a better 5 mile time than 10k which would throw it even further out but there is some doubt in my mind about the accuracy of the course for that one because it is so much faster than any other race I've done - though I was training more at that time.
Posted: 24/11/2004 at 16:44

It does seem to suggest that I need to put in a bit more endurance work. The 10k/half marathon comparison is really close, I'm only about 30 seconds off. My marathon time was way off, but that's not surprising as I have only run one and almost pulled out after losing almost 6 weeks training to injury and illness and crawled home in about 3:20. Encouraging to think that with the right endurance training before my next marathon, I should be able to knock at least 12 minutes off my last time though!
Posted: 24/11/2004 at 16:53

Foo Bar, no sorry! What are you suggesting? I'd like to think I work just as hard for both though!
Posted: 24/11/2004 at 17:30

completely off for me, I put in my 1500m time for last season and it reckons I should be running sub 34 for the 10k and I'm down to about 35/36, put in my most recent training time for 1500 and it reckons I should be doing almost 32 minutes.

About right with my 5k, 10k and 10 mile times though, my 10 mile time is a little slower comparatively but I've only done one. I'd say the calcs a little on the fast side though.
Posted: 24/11/2004 at 18:05

It better do - I will let you know on Sunday!
Posted: 24/11/2004 at 18:24

My 5k time predicts my marathon target time which is nice (but 16 minutes faster than current time)and is faster than my current times at all distances. Putting in my marathon time isn't too far out down to 10k but is significantly slower than actual 5k and 5m. I think I probably am biased towards the shorter distances though.
Posted: 25/11/2004 at 09:12

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