Race Time Predictor (5K, 10K, Half, Marathon)
Calculator ToolsPredict race times from one recent result
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All history →Race Time Predictor (5K, 10K, Half, Marathon) — at a glance
Turn one race result into predicted times for other distances.
10K in 55:00
Predict Times
Predicted marathon time
How to use it — step by step
A recent distance and the time you ran it in.
1
Enter your values
Fill in the fields. Default numbers are shown so you can see how it works.
2
Press Predict Times
The answer appears at once as large result cards.
3
Copy or share
Copy the result, or share a link that opens with your numbers filled in.
Pro tips
Small things that make the result better.
✦Use a recent, hard effort for the best prediction.
✦Long races need extra training the formula cannot see.
✦Predictions get less exact for far distances.
Quick facts
Freeno signup
Privateruns in your browser
Instantresult in a second
No limituse it as often as you like
Frequently Asked Questions
What is the Riegel formula?+
T2 = T1 × (D2 ÷ D1)^1.06. It scales your time for a different distance.
How accurate is it?+
Good for similar distances, and optimistic for a marathon predicted from a 5K.
Is my data safe?+
Yes. Everything runs inside your own browser. Your text, files and images are never uploaded to any server.
Is this tool really free?+
Yes — completely free, no signup, no watermark and no usage limit.
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