Marathon Finish Time Calculator
Predict a marathon time from a shorter race, and see the pace each segment needs.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
This Riegel-model estimate scales a recent race time by distance raised to the selected exponent. Use a representative, recent effort; training, endurance, course, weather, pacing and health can make actual marathon performance differ substantially. It is a planning estimate, not a guarantee.
Worked example
calculated with the default values below
Recent race distance 21.1 km · Race time — hours 1 h · Race time — minutes 45 min · Fatigue exponent 1.06 · Target distance Marathon Predicted finish time 3:38:55 · Predicted time 218.9 min · Required pace 5:11 · Required pace 8:21 · Halfway split 1:49:28
General background references
Disclaimer
These calculators give general mathematical results. They suit study, planning and estimation — verify anything that feeds a graded submission, a published figure or a financial commitment.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
t₂ = t₁ × (D₂ ÷ D₁)^e
- t₂
- predicted time for target distance, min
- t₁
- recent race time, min = 60h + m
- D₁
- recent race distance, km
- D₂
- target distance, km
- e
- fatigue exponent (≈1.06)
Riegel estimate: t₂ = t₁ × (D₂ ÷ D₁)^e; the default exponent 1.06 is a model parameter, not an individual guarantee. Actual performance depends on preparation and conditions.
Frequently asked questions
How does the Riegel estimate scale a half-marathon time to a marathon?
It multiplies the shorter time by (target distance ÷ recent distance) raised to the selected exponent. With exponent 1.06, doubling the distance multiplies time by about 2.09, not 2.11. The result is a model estimate and depends on representative recent performance and endurance preparation.