ZOVATOOL

Finish Time Calculator

Mode

Unit

What have you done so far?

Projection

Current pace
5:00 /km
Remaining distance
11.10 km
Remaining time
0:55:29
Finish total time
1:45:29
Finish clock time
12:02:14 AM
Pace used (remaining) /km
5:00
Avg speed
12.00 kph

How to use the Finish Time Calculator

  1. Enter a recent race distance and time.
  2. Select the target race distance (5K, 10K, half marathon, marathon, 50K, 50 mile, 100K, 100 mile).
  3. Calculator uses Riegel's formula (T2 = T1 × (D2/D1)^1.06) to predict finish time.
  4. Add training volume input for accuracy adjustment (predictions assume similar training).
  5. See predicted finish plus recommended target pace per km/mile.
  6. Compare against known finish-time benchmarks (Boston qualifier, sub-4 marathon, etc.).
  7. Adjust for elevation, heat, and course profile using built-in modifiers.
  8. Print a pace band with target splits for race day.
  9. Save for tracking prediction accuracy over multiple races.
  10. Use with the training log to see if training volume matches prediction confidence.
Advertisement
Ad space

Race finish time prediction: how accurate is Riegel's formula really?

Race prediction is the sport of speculating about future pain. Runners obsess over finish times months out — 'if I can run a 22:00 5K in April, what marathon time can I target in October?' Peter Riegel's formula from 1977 remains the gold standard: T2 = T1 × (D2/D1)^1.06, where T is time and D is distance. It's simple, empirical, and startlingly accurate under the right conditions.

The right conditions matter. Riegel's exponent of 1.06 was derived from world-class runners at similar training states across their competitive distances. Applied to trained runners predicting from 5K to half marathon, accuracy is ±2%. Applied to a 5K runner predicting a marathon without marathon-specific training (20+ mile long runs, race-pace tempos, fueling practice), the prediction is 5–15% optimistic. The formula doesn't know if you've run long.

Common benchmarks worth memorizing: sub-4 marathon = 9:09/mile (5:41/km) average pace. Boston qualifier for 35-year-old man = sub-3:00 marathon = 6:52/mile (4:16/km). Sub-2 half marathon = 9:09/mile (5:41/km). Sub-25 5K = 8:03/mile (5:00/km). These times are within reach for most healthy adults with 3–6 months of structured training and a weekly long run appropriate for the distance.

The 'wall' at mile 18–22 in a marathon is glycogen depletion, not fitness failure. Muscle glycogen stores are limited to about 400–500 g (1600–2000 kcal), enough for 90–120 minutes of hard running. Beyond that, the body relies increasingly on fat metabolism, which is slower. Race-day fueling — 30–60 g of carbs per hour via gels, chews or drink — is what lets trained runners hold marathon pace to the finish. Skip fueling and even a well-trained runner blows up at 20.

Prediction confidence increases with training volume similar to race demands. A runner logging 25 miles/week predicting a marathon is guessing. A runner logging 45–60 miles/week with three long runs of 18+ miles has a prediction confidence of ±3 minutes. The calculator's training-adjusted mode weights predictions by weekly mileage, longest recent long run, and race-specific workouts completed. Use it for planning, respect its assumptions, and always target a pace 5 seconds/mile slower than predicted for the first 3 miles — negative splits win races.