Free tool · Predictor
Race Time Predictor
One recent race tells you what you’re capable of at every distance. Enter it and see your equivalent times from the mile to the marathon, computed with Jack Daniels’ VDOT model.
Predictions use Jack Daniels’ VDOT model — the same equivalent-performance math coaches use, more accurate than a flat Riegel exponent across short and long distances. They assume you’re trained for the target distance; a marathon off low mileage runs slower than the equivalent predicts.
You could run
1 mile
6:09
6:09/mi
3K
12:11
6:32/mi
5Kyou ran
21:00
6:46/mi
8K
34:25
6:55/mi
10K
43:32
7:00/mi
15K
1:06:60
7:11/mi
10 mile
1:12:14
7:13/mi
Half marathon
1:36:28
7:22/mi
Marathon
3:20:41
7:39/mi
Stop calculating. Start training.
These numbers are the first 30 seconds of what Shed does.
Shed reads your Apple Health, grounds your VDOT in your actual training — not one race — and writes the whole block: every workout, every pace, adjusted as life happens. The calculator gives you a snapshot; Shed gives you the plan.
Get your plan on iPhoneEquivalent times, not promises
Equivalent race times answer “if I’m this fit, what could I run?” They line every distance up on the same fitness curve, so a 5K result projects a half and a marathon. The shorter and fresher the race you enter, the more honest the read on your current fitness.
The longer the prediction, the more training depth matters. A 5K reflects aerobic power you already have; a marathon also demands the endurance, durability, and fueling you only build with weeks of long runs. Treat longer predictions as targets to train toward, not times you can run cold.
Frequently asked
- How does the race time predictor work?
- It computes your VDOT (Jack Daniels’ fitness score) from the race you enter, then reads the equivalent time at each other distance off the same fitness curve. That’s more faithful across the 5K-to-marathon range than a single fixed Riegel exponent, which drifts at the ends.
- How accurate is a marathon prediction from a 5K?
- The equivalent assumes you’re trained for the marathon. If your long runs and weekly mileage aren’t there, your real marathon will be slower than the prediction — endurance and fueling, not just aerobic power, decide the back half. Use it as a ceiling, then build the training to reach it.
- What race should I base it on?
- Your most recent hard, even-effort race, ideally within 6 weeks. Shorter races (5K/10K) give the cleanest read on current fitness.