Predict your 5K, 10K, half marathon or marathon time from a recent race.
Adding more races helps build a more accurate picture of your fitness.
It starts from a recent race and uses an extended version of the Riegel formula, where the expected slowdown increases for the half marathon and marathon. It then adjusts for how hard you ran that race, the shoes you wore and, in Advanced mode, your weekly mileage and any other recent races you add.
Predictions are most reliable when your recent race was run all out, is close in distance to the race you are predicting, and you have done the training for the new distance. Predicting a marathon from a 5K is the least reliable, which is why the result is shown as a range from optimistic to conservative.
A race run at a controlled or easy effort understates your fitness. If you tell the predictor you had more in the tank, it estimates what you could have run all out and predicts from that instead.
Only if it looks low for the distance you are predicting. Long races, especially the marathon, punish low mileage, so the Advanced calculator slows the prediction when your weekly mileage is light for that distance. It never speeds you up for high mileage, and your age is not used as a penalty.
Yes, if you have them. In Advanced mode you can add other races from the last six months. More results give a better picture of your fitness and stop one unusually good or bad day from skewing the prediction.
Yes. Tell it which shoe you raced in and it removes that shoe's estimated benefit to find your underlying fitness. It can then show how your predicted time might change in a faster shoe. The Super Shoe Calculator goes into this in more detail.
Use the expected time to set your target, the conservative time if the course is hilly or hot or you are short on training, and the optimistic time only if everything has gone well. The Splits Calculator turns your target into km or mile splits.