Race Time Predictor (5K, 10K, Half, Marathon)
Calculator ToolsPredict race times from one recent result
Embed this tool on your websiteFree
- Choose how tall the frame should be.
- Press Copy code.
- Paste it into your page, blog, WordPress or Notion HTML block.
The tool runs inside your visitor's browser, nothing is uploaded, and a small "Powered by ToolCloak" line stays under it. The second line (script) is optional: it makes the frame fit the tool's height.
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History
All history →Race Time Predictor (5K, 10K, Half, Marathon) — at a glance
Turn one race result into predicted times for other distances.
How to use it — step by step
A recent distance and the time you ran it in.
Enter your values
Fill in the fields. Default numbers are shown so you can see how it works.
Press Predict Times
The answer appears at once as large result cards.
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.
Quick facts
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.