From a recent performance, estimate your times for 5K, 10K, half and marathon — via the Riegel formula. Then move on to your fuelling plan.
From a recent performance, the Riegel formula estimates your times at other distances (T₂ = T₁ × (D₂/D₁)^1.06).
Expected benefit: a number-backed target for your next race — and the time to drop into your fuelling plan.
Enter a recent performance to estimate your other times.
Setting a time goal 'by feel' usually means going out too fast and blowing up. A recent performance (a 10K, say) already holds the answer: it predicts fairly well what you can target at another distance — provided you use the right formula, not a generic table built for someone else's profile.
The Riegel formula — T₂ = T₁ × (D₂/D₁)^1.06 — models the speed lost as distance grows. The 1.06 exponent (from analysing thousands of races) captures the pace fade: doubling the distance doesn't double the time, it multiplies it by ~2.09. It's reliable between nearby distances and for a trained runner; it's a starting point, not a guarantee.
Start from a recent performance at a distance close to your target (a half predicts your marathon better than a 5K does). Riegel tends to be optimistic for the marathon from a short distance — add a margin if your weekly mileage is limited. Use the result to set your opening pace, then dial in nutrition with the fuelling plan.