How accurate is the race time predictor?

It’s a simple estimate. Accuracy is best when your input is a recent race effort on a similar course. Easy runs, hills, heat, wind, and fatigue can make the prediction too fast or too slow. Use it for planning, not as a guarantee.

What pace should I run for easy runs?

Use the Easy pace band shown (about 20–30% slower than your predicted race pace). Easy pace should feel conversational and sustainable. If it doesn’t, slow down regardless of the estimate.

How do I convert min per mile to min per km?

Divide your min/mi pace by 1.609 to get min/km. Multiply min/km by 1.609 to get min/mi. Example: 8:00 min/mi is about 4:58 min/km. The pace unit toggle does this automatically.

Free toolNo signupPace calculatorRace time predictormin/km & min/mi

Half Marathon Pace Calculator

Use this running pace calculator and race time predictor to calculate pace from distance + time, convert min/km and min/mi, and estimate a goal race finish time. Enter a recent run or race (distance + time), pick a goal distance like 5K, 10K, half marathon, or marathon, and get your pace, predicted finish time, and easy/tempo/interval training paces. Toggle miles or km, and convert min per mile to min per km (min/mi ↔ min/km) instantly. Estimates only. Not medical advice.

Enter a recent run (required)

Add distance + time. We’ll calculate pace, estimate a goal finish time, and suggest training paces.

Updates automatically

Distance

Short runs under 1 km (0.62 mi) make predictions less reliable. For best accuracy, use a recent race or hard effort.

Quick fill (common distances)

Time

Use mm:ss or hh:mm:ss (example 25:00 or 1:02:30). Shortcuts: 25 → 25:00, 930 → 9:30, 10230 → 1:02:30.

Goal distance (race time predictor)

This is the distance you want to predict (finish time + race pace).

Pace unit (min/km or min/mi)

Terrain (advisory only)

Terrain changes the advisory note only (math unchanged).

Results

Auto

Enter distance + time from a recent run to calculate pace. Then choose a goal distance to see an estimated finish time, predicted race pace, and training paces.

Methods & assumptions

This variant focuses on Half Marathon Pace Calculator.

This running pace calculator uses your distance + time to calculate pace. It then uses the Riegel formula to estimate a finish time for your chosen goal distance.

What you enter

Distance: The length of your recent run (km or miles).
Time: How long that run took (mm:ss or hh:mm:ss).
Goal distance: The race distance you want to predict (5K, 10K, half marathon, marathon, or custom).

What you get

Pace from your run: Your average pace in min/km or min/mi.
Estimated finish time: A predicted time for the goal distance.
Training paces: Easy/Tempo/Interval ranges based on your predicted goal race pace.

Formulas and assumptions