Marathon Time Predictor
Predict your marathon finish time from any known race result using the Riegel formula. Shows predicted times from 1 mile to full marathon.
How to use this tool
- Enter known race distance, finish time — minutes and finish time — seconds in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your marathon time and the full breakdown beneath it.
The Riegel formula — T2 = T1 × (D2/D1)1.06 — predicts race finish times across distances using one known result. It is widely used by coaches for race pacing.
Predictions assume equivalent conditions and fitness. Not a substitute for a structured training plan.
Frequently asked questions
- How accurate is the Riegel formula?
- For distances within 2–3x of your reference race it is generally accurate within 5%. Accuracy decreases for very long extrapolations.
- What exponent should I use?
- The standard exponent is 1.06. Some calculators use 1.07 for ultra distances. This tool uses 1.06.