Predict Your 5K Time From a Half marathon

How a Half marathon predicts your 5K

Predicting a 5K from a half marathon stretches across a wide range, from a ninety-minute effort down to one of fifteen to twenty-five minutes. The aerobic base you built for the half is a real asset, but a sharp 5K also asks for leg speed and a tolerance for going deep into the red, which a half does not test.

Read the result as a fitness-based target rather than a guarantee. A runner with good basic speed will often beat a half based 5K prediction, while a pure endurance runner with no fast training may land just behind it. The number tells you what your aerobic engine can support, the rest comes down to how comfortable you are running fast.

Endurance gives you the base, speed gives you the time

Your half marathon proves you have a strong aerobic system, which is most of what a 5K needs. But the 5K is run well above threshold, close to your VO2 max, and that gear only sharpens with practice. If your training is all steady miles, your 5K will sit near the prediction. If you add intervals at 5K pace or faster, you can drop under it.

The practical move is a few weeks of short, fast repetitions before you race the 5K. The endurance is already banked from your half. Speed work simply unlocks the top end and turns a conservative prediction into a personal best.

Want every distance at once? The race pace predictor shows your time for the whole range and prints a pace band, and the VDOT calculator turns this race into your training paces.