Plug in one recent running effort and we’ll estimate finish times across every standard distance from 1600 m to the full marathon. Three columns, Perfect, Normal, Poor, show the realistic range based on race-day execution, terrain, and weather.
Pick the distance you ran, then enter either a finish time or a pace, the other two fields will fill in automatically.
| Distance | Perfect day | Normal day | Poor day |
|---|
Three columns, three different days. Same fitness underneath, different execution on top.
Cool weather, flat course, fresh legs, well-fueled, even pacing, race-rested. Best 5–10% of your race outcomes, the day everything clicks.
What you should expect on most race days, reasonable conditions, decent fueling, a little wind or hills, slightly off pacing. Plan around this column.
Heat, hills, headwind, cramps, stomach issues, started too fast, undertrained for the distance. Not a disaster, just the rough end of the curve.
Each cell shows the projected finish time, plus the average pace per 400 m, per km, and per mile. The 400 m split is your interval-track reference. Per-km and per-mile are your race-day watch references.
The math behind this calculator is a Riegel-style power law: T2 = T1 × (D2/D1)k. The exponent k reflects how much you slow down as the distance grows. We use 1.03 for a perfect day, 1.06 for normal, and 1.12 for poor, bracketing the 1.05–1.07 range that fits most well-trained endurance athletes.
A few things this doesn’t know:
Use it as a sanity check and a pacing target, not a guarantee. For numbers grounded in your physiology, lactate threshold, VO2max, fat/carb crossover, come into the lab.
Same idea, more inputs, brings VO2max, weekly volume, and recent training into the projection.
Open → Boston qualifier (BQ)Marathon time vs. age-graded BQ standard, see how much margin you actually need.
Open → All calculatorsBack to the full catalog, 30+ endurance calculators across performance, fueling, swim, bike, run, strength.
Browse →Predictions are educated guesses from one effort. Threshold testing, VO2max, and metabolic profiling give you pacing zones grounded in your physiology, the kind of numbers that hold up on race day.
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