Altitude Pace Adjustment Calculator
Enter a race distance, the altitude, and a time. Choose whether you have a sea-level time and want the altitude-equivalent, or you raced at altitude and want the sea-level equivalent.
Direction
Altitude unit
Expected time at altitude
Pace at altitude: 5:22 /km. That is 7.9% slower than sea level, for Marathon.
This estimate uses a generic formula. Connect your Strava/Whoop/Garmin data for a version personalised to your actual training.
Get early accessWhy altitude slows you down
Thinner air at altitude carries less oxygen per breath, which lowers the maximal aerobic power (VO2max) you can sustain. For races lasting more than about two minutes, that is a bigger factor than the thinner air's one small benefit: slightly less aerodynamic resistance. The result is a real, physiology-driven slowdown that grows with both the altitude and the length of the race, since longer races draw more of their energy from aerobic metabolism.
How it is calculated
This calculator uses Péronnet, Thibault & Cousineau's (1991, Journal of Applied Physiology) theoretical model of altitude and running performance. Rather than reimplementing their full iterative model, which fits a runner's anaerobic capacity, aerobic power, and endurance from several performances, this calculator interpolates the percentage slowdown directly from the paper's own published tables of equivalent world-record performances at eight altitudes from sea level to 4,000 m, across 1,500 m, 5,000 m, 10,000 m, and the marathon. Your time is multiplied by 1 plus that percentage for the altitude direction, or divided by it for the reverse.
How to use the result
Use the altitude-adjusted time to set a realistic goal before a race or hard session at elevation, since pacing to your sea-level fitness at altitude is a reliable way to blow up. Use the sea-level equivalent to judge how a result at elevation compares to your flat-sea-level form, or to compare it fairly against a race predictor or VDOT table built from sea-level data. This model assumes you have not acclimatised; if you have spent a week or more training at the altitude already, expect the real slowdown to be somewhat smaller than the number shown here.
Sources and limitations: see our methodology.
Worked example
Take a runner with a 3:30:00 sea-level marathon who instead races the marathon at Mexico City (2,240 m).
The model predicts a 7.9% slowdown at that altitude for the marathon, giving an expected altitude time of 3:46:39. That is roughly 16:39 slower than their sea-level fitness alone would predict, and exactly the gap a flat sea-level goal pace would not account for.
FAQ
How much slower will I race at altitude?
It depends on both the altitude and the race distance: longer races slow down more at a given altitude, because they draw more energy from aerobic metabolism. As a rough guide from the model behind this calculator, a marathon at Mexico City's altitude (2,240 m) is predicted to be about 7.9% slower than sea level; a 5K at the same altitude is predicted to be about 7.3% slower. Enter your own distance and altitude for a specific estimate.
Is this calculator for acclimatised or unacclimatised runners?
Unacclimatised: the model is built from how barometric pressure reduces VO2max and air density on acute exposure, not from weeks of altitude adaptation. If you have trained at the altitude for a week or more before racing, your real slowdown will likely be somewhat smaller than this calculator predicts.
Why is there a slowdown even at a low altitude like 500 m?
The underlying model shows a small, continuous slowdown starting from sea level for races of 800 m and up; there is no altitude below which the effect simply switches off. At a few hundred metres the effect is small enough to be within normal day-to-day variation, but this calculator shows the computed number rather than rounding it to zero.
What altitude and distance range is this calculator valid for?
The source model was fitted to data between sea level and 4,000 m, and this calculator covers race distances from 1,500 m to the marathon. Outside either range you still get a result, with a warning, but treat it as a rougher extrapolation rather than a validated estimate.
Does this account for wind, heat, or course terrain at altitude?
No. This calculator isolates the altitude effect alone. Combine it with the Heat Pace Adjustment or Grade-Adjusted Pace calculators if the race in question also has challenging weather or a hilly course.