"You could run a 1:42 half today." Where does a number like that come from? Two pieces of well-established running math: VDOT and the Riegel formula. Here's how they work — and why we always show a range, never a single number.
VDOT: one number for your fitness
VDOT comes from Jack Daniels' Running Formula. It's essentially a VO₂max-equivalent derived from race performance rather than a lab test. Plug in a recent result — say a 22:30 5K — and you get a single number summarising your current aerobic fitness. Higher is fitter.
The power of VDOT is comparison. Two runners with the same VDOT should, in theory, race equivalent times across distances. It puts a 5K, a 10K, and a marathon on one scale, which is why coaches use it to set training paces.
Riegel: predicting across distances
The Riegel formula extrapolates a time at one distance to another:
T₂ = T₁ × (D₂ ÷ D₁)^1.06
The exponent 1.06 captures a simple truth: you slow down a little as distance grows. RUNNIQ uses this exact formula — and cross-checks it against VDOT — inside the app. Our free race time predictor runs the same math so you can try it without signing up.
Why a range, not a number
A single predicted time is seductive and misleading. Predictions assume two things that often aren't true: that conditions match, and that you've done the specific training for the target distance. A blazing 5K does not mean you're ready to run the equivalent marathon — the endurance still has to be built.
That's why both the app and the tool show a band, and why the band gets wider the further the prediction is from the result you entered. Predicting a 10K from a 5K is reliable; predicting a marathon from a 5K is a hopeful estimate at best.
From prediction to plan
A prediction tells you where you are. A plan gets you somewhere better. Once you know your VDOT, the next step is training that targets the gap — paced precisely to your zones. See how pace zones work, or jump straight to a 10K plan built around your current fitness.
Curious what you'd run today? Try the predictor, then build the plan to make it real.