Race Time Predictor
Predict race times from a recent result.
Enter your values
Enter the recent race distance in km.
Enter the hours you are working with.
Enter the minutes you are working with.
Enter the seconds you are working with.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Predicted marathon
- 3:33:55
- Predicted half marathon
- 1:42:36
- Predicted 10K
- 46:30
- Predicted 5K
- 22:18
- Predicted mile
- 6:42
- Current pace
- 4:39 per km
| Distance | Predicted time |
|---|---|
| 1 mile | 6:42 |
| 5K | 22:18 |
| 10K | 46:30 |
| Half marathon | 1:42:36 |
| Marathon | 3:33:55 |
Quick answer
Riegel's formula predicts race time as T₂ = T₁ × (D₂/D₁)^1.06 across distances.
T₂ = T₁ × (D₂ ÷ D₁)^1.06
At a glance
| What it does | Predict race times from a recent result. |
|---|---|
| Category | Fitness |
| Inputs needed | Recent race distance, Hours, Minutes, Seconds |
| Main output | Predicted marathon |
| Formula | T₂ = T₁ × (D₂ ÷ D₁)^1.06 |
| Cost | Free — no sign-up, no download |
How to use the Race Time Predictor
- 1Enter the distance of a recent race in kilometres.
- 2Enter your finishing time.
- 3Read predicted times for other distances.
Inputs explained
- Recent race distance(km)
- Enter the recent race distance in km.
- Hours
- Enter the hours you are working with.
- Minutes
- Enter the minutes you are working with.
- Seconds
- Enter the seconds you are working with.
Worked example
Using the values the calculator loads with:
Inputs
- Recent race distance10 km
- Hours0
- Minutes46
- Seconds30
Results
- Predicted marathon3:33:55
- Predicted half marathon1:42:36
- Predicted 10K46:30
- Predicted 5K22:18
- Predicted mile6:42
- Current pace4:39 per km
Frequently asked questions
How accurate is Riegel's formula?
Good within a factor of about 3× in distance. Marathon predictions from a 5K tend to be optimistic without marathon-specific training.
Why the 1.06 exponent?
It reflects the empirical slowdown as distance grows; well-trained endurance runners are closer to 1.05.
What do I need to enter into the Race Time Predictor?
Just 4 values: recent race distance, hours, minutes, seconds. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Race Time Predictor work out the answer?
Riegel's formula predicts race time as T₂ = T₁ × (D₂/D₁)^1.06 across distances. It applies the formula T₂ = T₁ × (D₂ ÷ D₁)^1.06 and shows the working so you can check each step by hand.
Is the Race Time Predictor free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.