Race split calculator

Turn a goal time for a 5K, 10K, half marathon or marathon into a split for every kilometre or mile, at an even pace or with a slightly faster second half.

How the calculator works

Choose your race, your goal time and a pacing plan. For an even pace, every kilometre or mile takes the same time. For a negative split, the second half is run a set percentage faster than the first, and both halves still add up to your goal time.

For a 3:45:00 marathon with the second half 1% faster, the first half is about 1:53:04 and the second about 1:51:56. Each row of the table shows that kilometre's split and the elapsed time, and the last row includes the shorter final segment.

Why a slightly faster second half

Starting a little under goal pace is a common way to protect the second half of a long race, when fatigue makes the same pace cost more. A plan of 1–2% faster is small: for a 3:45 marathon, 1% is about 68 seconds between the halves. Larger gaps mean a slower start than many runners can stick to.

Use the plan for the halves, not for every kilometre. Hills, turns, wind and crowded water stations will move individual splits.

Is the goal itself realistic?

Splits assume the goal is right. To see what a recent race suggests, use the race time calculator. To check a pace for a single distance, use the pace calculator.

From splits to a race plan

We make coach steve, an AI running coach you can text. Ask about your goal and it is designed to answer from your available training data, with anything missing made clear.

Common questions

Can I print the splits?

Yes. Open the table and print the page, or write the halves and a few key distances on your hand or a pace band.

Why are my watch splits different?

Watches measure distance by GPS, which often reads a little long over a marked course. Your watch may show each kilometre slightly early.

Where is my goal saved?

Nowhere. The calculator keeps it in the page while it is open.