It uses the Riegel formula, T2 = T1 x (D2/D1)^1.06, proposed by engineer Peter Riegel. The formula scales a recent race time to a new distance with a fatigue exponent of 1.06 that models how pace slows as distance grows. It assumes you are properly trained for the target distance.
Yes, and the half marathon is generally the most reliable single source distance because it is closest to the marathon in duration and effort. Enter your half time and read the marathon row. The prediction still assumes you have done marathon-specific endurance work.
The Riegel model assumes equal endurance preparation at every distance. A 5K mostly tests speed, while the marathon tests aerobic endurance, fueling and long-run volume. If your weekly mileage is modest, the prediction skews optimistic, and the shorter the source race, the bigger the skew.
The results table shows the required pace next to every predicted time, in min per km or min per mile via the toggle. The marathon is 42.195 km, about 26.2 miles, so holding that pace evenly carries you to the predicted finish.
It depends on your age and the standards of each race. The marathon row links straight into the Majors Qualification Checker, which grades the time against the qualifying, good-for-age and priority standards of all eight Abbott World Marathon Majors.
Yes, the formula works in both directions. Enter your marathon time and the shorter rows show equivalent times, which is useful for setting tune-up race targets during a training block.