Should my 5K be exactly half my 10K time?

No, it should be faster than half. A shorter race lets you hold a quicker pace, so Riegel multiplies your 10K by about 0.48, predicting a 5K nearly a minute faster than a flat halving would.

How accurate is a 10K to 5K prediction?

Very. The distances are close and share the same aerobic demands, so the prediction is usually within fifteen to twenty seconds for most runners.

Why might I beat my predicted 5K?

Because the 5K is short enough to race near your limit. Runners with good leg speed often dip under the prediction, especially after a few weeks of faster interval work.

Predict Your 5K Time From a 10K

Ran a 10K lately? Enter your time to see what it predicts for the 5K, plus the pace you would need to hold.

Your 10K time

min

sec

Pace in

Predicted 5K time

21:35

That is 6:57 per mi.

Worked example

A 10K of 45:00 predicts a 5K of about 21:35, a pace of 6:57 per mi. Change the time above to run the same math on your own result.

How a 10K predicts your 5K

Predicting a 5K from a 10K is one of the safer estimates the calculator makes. You are halving a distance that sits right next door, and both races draw on the same aerobic strength. Your 5K should come out meaningfully faster per mile, because half the distance lets you hold a pace you could never sustain for the full 10K.

The result is a dependable target. If anything, a runner with good basic speed can beat a 10K based 5K prediction by a few seconds, since the 5K is short enough to push closer to the red line. Runners who are pure diesel engines, strong but without much top gear, will land right on the number.

Your 5K should be faster than half your 10K

A tempting shortcut is to halve your 10K and call that your 5K, but that overestimates how slow you will be, because pace and distance do not trade off in a straight line. Riegel multiplies your 10K by about 0.48 rather than a flat 0.5, which captures the fact that a shorter race lets you run faster the whole way.

So a 45:00 10K does not predict a 22:30 5K, it predicts closer to 21:35. That difference, nearly a minute, is the speed you unlock by only having to hold the pace for five kilometers instead of ten. If your 5K comes out slower than this, you likely have more top-end speed to find with a little faster training.

Want every distance at once? The race pace predictor shows your time for the whole range and prints a pace band, and the VDOT calculator turns this race into your training paces.

Related predictions

10K to 5K questions

Should my 5K be exactly half my 10K time?: No, it should be faster than half. A shorter race lets you hold a quicker pace, so Riegel multiplies your 10K by about 0.48, predicting a 5K nearly a minute faster than a flat halving would.
How accurate is a 10K to 5K prediction?: Very. The distances are close and share the same aerobic demands, so the prediction is usually within fifteen to twenty seconds for most runners.
Why might I beat my predicted 5K?: Because the 5K is short enough to race near your limit. Runners with good leg speed often dip under the prediction, especially after a few weeks of faster interval work.