Marathon Time Prediction from a 25-Minute 5K
A 25-minute 5K predicts a marathon finish time of approximately 3 hours and 53 minutes.
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.
If you run a 25-minute 5K, this tool predicts your potential marathon finish time using the Riegel endurance formula.
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.