Half Marathon Time Predictor
Estimate a half-marathon finish time from a recent race, see the required kilometre and mile pace, and adjust the plan for distance-specific readiness.
Written and checked by TheToolNet Editorial Team · Last reviewed: October 2, 2026 · Editorial method
This calculator may be inaccurate and cannot judge whether running a half marathon is safe for you. It does not replace a doctor, coach, or individualized training plan. Consult a real doctor before strenuous exercise if you have symptoms, a health condition, are pregnant, or have been advised to limit activity.
Predict your half-marathon time
Choosing the recent result
A recent 10K is a useful starting point because it is closer to half-marathon demands than a short sprint. A 5K can still estimate the time, but it says less about sustained endurance. Use a measured course and an honest effort under reasonably comparable conditions.
Why the calculator exposes an adjustment
Hidden “smart” corrections can look more certain than they are. This tool shows the formula-only result and lets you add a visible percentage if your long-run preparation, course familiarity, or endurance base is weaker than the equation assumes. It never subtracts time automatically.
Practical limitations
The Riegel endurance model describes performance across distances. It does not measure heat, hills, wind, fueling, injury, sleep, accumulated fatigue, or race execution. Use the result as a planning reference and compare it with recent long runs and training.
Frequently asked questions
What adjustment should I choose?
There is no universal percentage. Leave it at zero to see the pure formula. Any addition should reflect your own conservative planning, not a medical or coaching prescription.
Can I predict from a treadmill run?
You can enter the result, but calibration, cooling, incline, and indoor pacing may not match the target course.
Can I predict other distances?
Use the general race time predictor calculator for custom targets.