Not medical advice.These estimates are for general informational use only and aren't a substitute for professional medical advice, diagnosis, or treatment. Consult a qualified healthcare provider before changing your diet, exercise, or medication.

How the pace and speed are worked out

Pace is simply your finish time divided by the distance. Enter a result and the tool reports it two ways — minutes per kilometre and minutes per mile — plus average speed in km/h. Distance is held internally in metres and time in seconds, so the presets (5K, 10K, half and full marathon) and any custom distance all use the same exact arithmetic. A half marathon is taken as 21,097.5 m and a marathon as 42,195 m, the official IAAF/World Athletics road distances.

VDOT and equivalent race times

The VDOT score is an estimate of running fitness derived from a single race performance. It combines the velocity-to-oxygen-cost relationship and the fraction of maximal oxygen uptake that can be sustained for a given duration, following the model inDaniels & Gilbert, "Oxygen Power" (1979), popularised by Jack Daniels inDaniels' Running Formula. A higher VDOT means a faster equivalent performance across distances.

The equivalent race times table uses Riegel's endurance model: predicted time T₂ = T₁ × (D₂ / D₁)^1.06, where the exponent 1.06 reflects how pace slows as distance grows. This comes fromPete Riegel, "Athletic Records and Human Endurance", American Scientist 69(3), 1981. The prediction is most reliable when the target distance is close to the one you ran and when you are appropriately trained for it; extrapolating from a 5K to a marathon assumes marathon- specific endurance you may not yet have.

Karvonen training heart-rate zones

Zones are built on the heart-rate-reserve (Karvonen) method: target = resting HR + intensity × (maximum HR − resting HR), fromKarvonen MJ, Kentala E, Mustala O. Ann Med Exp Biol Fenn, 1957. Maximum heart rate is estimated with the Tanaka formula, 208 − 0.7 × age, fromTanaka H, Monahan KD, Seals DR. J Am Coll Cardiol, 2001, which fits the population better than the older 220 − age rule. The five zones use heart-rate-reserve bands of 50–60%, 60–70%, 70–80%, 80–90% and 90–100%.

All calculations run entirely in your browser; your inputs are saved only to this device's local storage and are never sent anywhere.

Frequently asked questions

Why are my predicted longer-distance times slower than a flat extrapolation?

Because pace naturally fades as distance increases — you cannot hold 5K pace for a marathon. Riegel's exponent of 1.06 builds that fade in, so doubling the distance adds more than double the time. That is the model working as intended, not an error.

How accurate are the race predictions?

They are best treated as a ceiling that assumes you are specifically trained for the target distance. A recent, all-out race over a similar distance gives the most trustworthy projection. The further you extrapolate — especially from short races to the marathon — the more the result depends on endurance and fuelling that a short race does not test.

Should I use the estimated maximum heart rate for my zones?

The Tanaka estimate (208 − 0.7 × age) is a population average; individual maximums vary by roughly ±10 bpm or more. If you know your true maximum from a field test or lab measurement, your zones will be more accurate using that value. The zones here are a general training reference, not medical guidance.

Is my data stored or shared?

No. Every calculation happens on your device and your last-used inputs are kept only in this browser's local storage. Nothing is uploaded, and there is no account.