The Race Predictor takes one race result you already have and answers two questions: how strong is your aerobic engine right now (your estimated VO2 Max), and what times you could expect to run at every other distance — from a 400m sprint all the way to a 100-mile ultra.
Behind the scenes it uses the well-established Daniels & Gilbert running model. You give it a distance and a finish time; it works backward to your VO2 Max, then forward again to project equivalent performances, paces, and the aerobic/anaerobic balance of each event.
Quick Start
Pick your Distance. Choose the event you actually raced from the dropdown (e.g., 5k).
Enter your Time as hours : minutes : seconds. For a 21:30 5K, that's 0 h, 21 m, 30 s.
Set Sex and Age. These refine the VO2 Max formula and your fitness rating.
Choose lbs or kg, then your Weight. Weight feeds directly into the calculation, so be honest here.
Press “Predict Your Race Times.” Your VO2 Max, fitness category, and the full prediction table appear below.
Tip: Your entries and your last result are saved in your browser automatically, so the page remembers you next visit. Use Clear saved to wipe them.
The Inputs Explained
Distance: 21 standard events from 400m to 100 Mile. Pick the one you raced — this is the anchor for everything else.
Time (h : m : s): Your finish time for that race. Use chip/net time if you have it, not gun time.
Sex: The model uses a sex-specific baseline constant (91.736 for men, 88.02 for women) reflecting average physiological differences — not effort or ability.
Age: Does not change the predicted times. It is used only to grade your VO2 Max against age-appropriate norms for the fitness label.
lbs vs kg: Tells the calculator which unit your weight is in so it can convert correctly.
Weight: Because VO2 Max is measured per kilogram of body weight, this number matters. Use your race-day weight for the truest result.
Reading Your Results
After you submit, three things appear:
VO2 Max in ml/kg/min — your estimated aerobic ceiling from the race you entered.
Fitness category — a word (Average, Good, Excellent, Athlete…) placing that VO2 Max in context for your age and sex.
The prediction table — equivalent performances at every distance, grouped as Sprints, Middle, Medium, Long, and Ultra. Your entered distance is highlighted in yellow as the reference row.
The table has five columns:
Column
Meaning
Distance
The event being projected.
Time
Predicted finish time (HH:MM:SS) at equal fitness.
Pace
Average pace in minutes per mile for that prediction.
% Anaerobic
Share of energy from the fast, oxygen-independent system.
% Aerobic
Share of energy from the oxygen-using system.
What Is VO2 Max?
VO2 Max (maximal oxygen uptake) is the most you can take in, transport, and use per minute, in milliliters of oxygen per kilogram of body weight per minute. It is the single best physiological predictor of distance-running potential — the size of your aerobic engine.
When you race, you hold a percentage of that ceiling for the whole event: nearly 100% in a mile, roughly 93–97% in a 5K, about 75–85% in a marathon. Because that relationship is well-mapped, a distance plus a time is enough to estimate VO2 Max — no lab required.
Aerobic vs Anaerobic Balance
The two right-hand columns show the energy-system mix of each event. A 400m is heavily anaerobic (fast, fueled without oxygen, unsustainable); a marathon is almost entirely aerobic. This matters for two reasons:
Prediction accuracy: events with a similar balance predict each other best. A 5K (~93% aerobic) gives a trustworthy 10K estimate; it gives a much rougher guess at your 800m.
Training focus: the balance tells you which system a goal race rewards, so you know whether to emphasize speed/anaerobic work or aerobic endurance.
Rule of thumb: the further the predicted event sits from your entered event on the aerobic/anaerobic scale, the more you should treat its number as a ballpark, not a promise.
Fitness Rating Scale
Your VO2 Max is graded into one of seven bands, scaled by age and sex: Need Improvement → Below Average → Average → Above Average → Good → Excellent → Athlete. The thresholds drop with age (a VO2 Max of 45 is “Good” for a 50-year-old man but only “Above Average” for a 25-year-old) and run a few points lower for women at each tier, reflecting population norms rather than potential.
Getting Accurate Predictions
Use a recent race. Fitness moves; last month beats last year.
Race all-out. The model assumes a maximal, evenly-paced effort. A training run or a pacing job will understate you.
Stay near your event. Predict distances close to the one you entered for the tightest numbers (the calculator itself warns that an 800m won't accurately predict a marathon).
Use race-day weight and chip time.
Prefer flat, fair conditions. Hills, heat, humidity, altitude, and wind all slow you and will under-report your true VO2 Max.
No recent race? Use the tip in the right-hand card: run a hard 1–3 miles on a track and enter that — solid effort, but don't wreck yourself chasing the last second.
Saved Data & Privacy
Your inputs and your most recent result are stored in your browser's localStorage so the form stays sticky and your last prediction reappears on return visits. The Clear saved button removes both. Nothing is transmitted anywhere — all of it stays on your device.
The Math Behind It
For the curious, the engine runs in two steps:
Step 1 — VO2 Max. Convert your time to seconds, scale it by a distance-specific factor to get a “VO2-equivalent” time in minutes, then apply the regression:
Men: VO2 Max = 91.736 − (0.1656 × kg) − (2.767 × min) Women: VO2 Max = 88.02 − (0.1656 × kg) − (2.767 × min)
Step 2 — Predictions. Each target distance has its own empirically-derived factor. Holding your VO2 Max constant, the engine solves that factor for time, producing the equivalent performance, pace, and energy-system split shown in the table.
Companion Tools
This predictor works from a single race. For a fuller picture, pair it with:
