Race Time Predictor
Predict 5K, 10K, half marathon, and marathon times from one result.
min
sec
How it works
Uses the Riegel formula: T₂ = T₁ × (D₂ ÷ D₁)^1.06. It assumes you train well for the longer distance; marathons in particular often run slower than predicted without enough long runs. Times are shown as hours:minutes:seconds.
FAQ
Is this calculator free?
Yes. No signup is needed and nothing you enter is stored.
Is the result exact?
Results are rounded for display. For financial, medical, or legal decisions, confirm with a professional.
Do my numbers leave my device?
No. The calculation runs in your browser.