Marathon Finish Time Predictor
Predict your marathon finish time from a recent race with Riegel’s formula (adjustable fatigue exponent), Daniels’ VDOT equivalence or Tanda’s training formula — with goal pace, a per-km or per-mile pace band, even and negative-split plans and 5 km checkpoints.
How it works
Riegel: marathon = race time × (42195 ÷ race distance in m)^k, k = 1.06 standard · VDOT: the marathon time whose Daniels VDOT equals your race’s VDOT · Tanda: marathon pace (s/km) = 17.1 + 140 × e^(−0.0053 × weekly km) + 0.55 × training pace (s/km) · goal pace = time ÷ 42.195 km · negative split: first half pace = 2p ÷ (2 − x), second half = first × (1 − x)
Pick a recent race and its time, and the calculator scales it up to 42.195 km. Peter Riegel’s model raises the distance ratio to a fatigue exponent: 1.06 fits well-trained runners, but the marathon punishes low mileage, so 1.07–1.10 (or your own value) gives a more honest target if your long runs are thin. The VDOT method instead works out Jack Daniels’ fitness score for your race and finds the marathon time with the same score; it tends to be a little kinder to fast short-race times. “Average” splits the difference, and “Training” uses Tanda’s formula, which needs no race at all — just your average weekly distance and training pace over the last eight weeks. A half marathon within the last month is the single best predictor because it shares the marathon’s aerobic demand. The pace band lists the elapsed time at every kilometre or mile, side by side for even pacing and for a negative split, where the second half is run a little faster (2% by default) while the finish time stays the same. Under More options you can build the band for your own goal time instead of the prediction.
Worked example
A 1:40:00 half marathon (6,000 s) at k = 1.06: 6,000 × (42195 ÷ 21097)^1.06 = 6,000 × 2.085 ≈ 12,510 s, or 3:28:30 — a goal pace of 4:56 /km (7:57 /mi). The same race is a VDOT of about 45.1, and the marathon with the same VDOT is 3:27:47, so the two methods agree within a minute. With the default 2% negative split the first half takes 1:45:18 at 4:59 /km and the second 1:43:12 at 4:53 /km, passing 30 km in 2:28:51.
Sources: Riegel, “Athletic Records and Human Endurance” (American Scientist, 1981) · Daniels & Gilbert, Oxygen Power (1979) — VDOT equations · Tanda G. Prediction of marathon performance time on the basis of training indices. J Hum Sport Exerc 2011;6(3):511–520
Frequently asked questions
Which race should I use to predict my marathon?
A half marathon within the last month is ideal. Shorter races over-predict because they lean more on speed than on the marathon’s fuel and durability demands.
Why offer different endurance factors?
The standard 1.06 assumes marathon-specific training. If your weekly mileage and long runs are limited, 1.08–1.10 better reflects the extra slowdown you will feel after 30 km. The exponent table shows how much each step changes your time.
What is the difference between Riegel and VDOT?
Riegel is one power law applied to any distance. VDOT is Jack Daniels’ estimate of your effective aerobic capacity from the race, converted back into the marathon time that needs the same capacity. They usually agree within a couple of minutes from a half marathon and drift further apart from a 5 km.
What is a negative split and should I plan one?
It means running the second half faster than the first. A small negative split of 1–3% protects your glycogen early and is how most marathon records are run. Enter the percentage under More options; the finish time stays the same, only the halves change.
Can I run faster than the prediction?
Yes, with disciplined pacing, fuelling and a strong build-up. The prediction is a realistic ceiling for your current fitness, not a hard limit.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.