Enter one recent race result. Get predicted times at every other distance — 5K through marathon, plus any custom distance you want to target.
hr
min
sec
1 Mile
6:37
5K(your input)
22:00
10K
45:52
15K
1:10:30
10 Mile
1:15:57
Half Marathon
1:41:12
Marathon
3:31:00
50K
4:12:36
Predictions use Riegel's formula (T₂ = T₁ × (D₂/D₁)^1.06). Most accurate for target distances within 2-3× of your input. For marathons extrapolated from shorter races, assume you'll need endurance-specific training to hit the prediction.
Predictions are a snapshot. Threshold is the training.
Threshold builds your weekly plan toward a target race — tempo runs, long runs, and VO₂ intervals, all calibrated to your current pace. Watch the prediction actually happen.
Try Threshold freeThis calculator uses Peter Riegel's 1977 endurance formula:
Where T₁ is your known race time, D₁ is the distance you raced, D₂ is the distance you're predicting, and 1.06 is the empirically-fit fatigue exponent. Riegel derived it from thousands of race performances across distances; it's been validated repeatedly and remains the most widely-used endurance prediction formula.
Riegel is most accurate when the target distance is within about 2-3× the input distance. A 5K result predicts 10K very reliably. A 5K predicting marathon is more speculative — you can physiologically hit the predicted pace, but only with marathon-specific training.
Feed this calculator actual race results — not training runs or tempo efforts. Riegel assumes a maximal effort at the input distance. A hard training run won't predict your race potential; it'll predict what happens if you run the target distance at tempo effort (significantly slower than your actual capability).
Threshold builds the weekly training that turns a prediction into a PR. Your plan adapts to recovery, progresses with your pace, and keeps you on track to race day.
See Threshold