Enter your latest race result to see your estimated finish times for the 5K, 10K, half-marathon, and marathon. You’ll get a range based on the Riegel and Cameron models, along with VDOT training paces.
Your recent result
We predict equivalent finish times at the other distances using two independent models.
Prediction models
Originally published in Runner’s World. The formula T₂ = T₁ × (D₂/D₁)^1.06 gives accurate results for race durations between 3:30 min and 3:50:00 h. Outside that window, extrapolations become less reliable.
Derived from nonlinear regression on world-record performances from 400 m to 50 miles. Uses a distance-specific fatigue factor: T₂ = T₁ × (D₂/D₁) × f(D₁)/f(D₂) where f(d) = 13.497 − 0.0000304d + 835.7/d^0.79. Tends to be more conservative than Riegel for longer target distances.
Predicted finish times
20:00
41:40–41:42
1:31:51–1:32:00
3:11:49–3:15:11
Reading the interval
Each card shows a time range spanning both models. For a longer target race, Riegel is the optimistic bound and Cameron is the conservative one. For a shorter target, the roles reverse.Training paces
VDOT 49.8Derived from the race you entered using the Jack Daniels VDOT method. For more accurate marathon-pace training, enter a marathon result instead.
Conversational long runs and recovery. Builds aerobic base.
Goal marathon race pace. Sustained medium-long runs.
Comfortably hard tempo runs and cruise intervals.
Hard 3–5 min repeats to maximise VO₂max stimulus.
Short 200–400 m reps at mile effort with full recovery.
Predictions work best if your race time is between 3:30 and 3:50, and your goal distance is similar to what you ran. If you try to predict a marathon from a 5K, it assumes you have the needed endurance. Without long-run training, your actual finish time is usually slower than the model predicts.
Riegel (1977) scales time by distance raised to the 1.06 power — a simple, widely-used rule. Cameron (1998) fits a distance-specific fatigue factor from world-record data and is usually a touch more conservative for longer targets. We show both so you can read the spread between them as a confidence range.
Each card highlights how the two models differ. For longer races, the Riegel estimate tends to be more optimistic, while Cameron is more conservative. For shorter races, this switches. Try using the range as a realistic guide instead of relying on a single number.
Yes, but be careful. The more you try to predict from a shorter race, the more your result relies on endurance that the short race did not measure. For the most reliable marathon prediction, use your recent half-marathon or 10K time.
They come from your VDOT — Jack Daniels' measure of running fitness derived from the race you entered. The five zones (easy, marathon, threshold, interval, repetition) provide target pace ranges for each workout type, in your chosen km or mile unit.