Endurometry
Use a recent 10K or half in the race predictor. Believe Daniels if you have trained 32 km+; if your longest run is under 25 km, add minutes or read the 1.10 column. 10K 50:00 → 3:49:34 (Daniels), 4:03:39 (1.10). A 4:00 marathon is 5:41/km.
Last updated October 5, 2026
This is the how-to. The models themselves are in race time prediction explained. You need one honest race and an honest longest run — not a time you like the sound of.
Pick the known race
Prefer a 10K or half from the last few months, on a course that resembles the marathon (not a net-downhill 5K). Enter it in the race time predictor. Official marathon distance is 42.195 km, not 42.
Numbers that match the calculator
| Known | Daniels marathon | Pace | 1.10 bound |
|---|---|---|---|
| 10K 48:30 | 3:42:54 | 5:17/km | 3:56:20 |
| 10K 50:00 | 3:49:34 | 5:26/km | 4:03:39 |
| Half 1:45:00 | 3:37:50 | 5:10/km | 3:45:04 |
| Half 2:00:00 | 4:07:45 | 5:52/km | 4:17:14 |
A 2:00 half is 5:41/km — the same even pace as a 4:00 marathon. Riegel still adds time because the second 21 km costs more than the first. That is why 2:00 does not become 4:00 on the page.
Adjust for training, not for hope
Daniels assumes you have trained the target. If your longest run is under about 25 km, do not subtract from 3:49 — add. Many first marathons sit nearer the 1.10 column (4:03 from a 50:00 10K) than the headline. If you have several 30–35 km long runs and the 10K was recent, Daniels is the better start. Heat, hills or a tight cutoff: check the cutoff calculator before you lock a goal.
Turn the finish into a pace you can hold
A 4:00 goal is 5:41/km (9:09/mi). A 3:42:54 Daniels finish is 5:17/km — only useful if the long runs support it. Print even splits on the pace calculator, then follow marathon pace strategy: first 10 km should feel too easy. Fuel 60–90 g carbohydrate per hour from the first hour, not from km 30.
Related Tools
Race Time Predictor
Predict your finish time at any distance using the Riegel power law and the Daniels–Gilbert VO2max model.
Running Pace Calculator
Enter distance and finish time to get your pace per km and mile, average speed and per-kilometre splits.
Race Cutoff Time Calculator
Compare a planned even pace plus start-line delay with the course time limit, and see a linear checkpoint sketch — not the official race table.
Related guides
Race time prediction explained
How Endurometry scales a known race to another distance: Daniels–Gilbert as the headline, Riegel 1.06 as a check, 1.10 as a cautious longer-race bound.
Marathon Pace Strategy
How to pick a realistic marathon goal pace from a recent race, why even splits beat fast starts, and how to hold pace without watching your watch all day.
How race cutoffs work
Finish cutoff versus intermediate gates, gun time versus chip time, and the same 6-hour marathon numbers the cutoff calculator prints: 6:30/km, 60 s delay, 4:35:16 finish, +85 min buffer, 8:32/km sweep.
How the numbers are calculated
Frequently Asked Questions
Should I use a 5K to predict the marathon?
You can, but the gap is large. A 10K or half is a better known race. From 5K 25:00 the Daniels half is already 1:55:04 — treat a 5K→marathon figure as a sketch.
Why is a 2:00 half not a 4:00 marathon?
Riegel and Daniels both add fatigue on the second half of the distance. 4:07:45 (Daniels) is the scaled estimate; 4:00 would require more endurance than the half alone shows.
What if I have never run a race?
The model has nothing honest to scale. Time a 5K or 10K as a race effort first, then predict.
Do I aim at Daniels or 1.10 on the day?
Aim at a pace you have rehearsed. Use Daniels as the fitness ceiling and 1.10 (or slower) as the plan if the long runs are thin.
Want a new tool or fix?
Tell us which calculator, pace chart or fix would help — we build what runners ask for. Replies usually come back in 1–2 days.