Marathon split planner
Enter your goal time and pick a distance, then choose an even pace or a negative split, where the second half is a set percentage faster than the first. The table lists each split, pace and the clock time at every kilometre or mile.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose the distance and enter the goal time in hours, minutes and seconds.
- Pick an even pace, or a negative split and how much faster the second half should be (3 percent is a gentle start).
- Choose kilometres or miles and read the table.
How it works
The halfway point is half the race distance. The first half is run at one pace and the second at a slightly faster one. Clock time at any point is worked out from those two paces, and each row is the difference between two marks. The halfway point falls inside a kilometre or mile, so the row containing it mixes both paces.
Worked example
A 4:00:00 marathon with a 3 percent negative split: the first-half pace is 2 × 14,400 s ÷ (42.195 × 1.97) = 346.5 s/km (5:46), and the second-half pace is 346.5 × 0.97 = 336.1 s/km (5:36). The halfway time is 21.0975 × 346.5 = 7,310 s, or 2:01:50. An even pace would be 341.3 s/km (5:41) all the way.
Tips
- Treat the plan as a guide: hills, wind and crowds change real splits.
- Check the course profile and adjust your plan for big climbs or descents.
- Practise your goal pace in training before race day.
Frequently asked questions
What is a negative split?
A negative split means running the second half of a race faster than the first. Here the first half runs at one steady pace and the second half at a pace the chosen percentage faster, and the two are balanced so the whole race comes out at your goal time.
How is the pace worked out for a negative split?
If the second half is d percent faster, the first-half pace is 2 × goal time ÷ (distance × (2 − d)), with d as a fraction, and the second-half pace is that times (1 − d). The two halves then add up to the goal time exactly.
Why is the last split short?
A marathon is 42.195 km, which is 42 full kilometres plus 195 m, or 26.2188 miles. The last row covers the partial distance, and its pace is shown per full kilometre or mile so it compares with the others.
Is a negative split better than an even pace?
Neither is guaranteed. Many coaches advise an even or slightly negative split because starting too fast tends to cost more time later. This tool just plans the numbers. Your own fitness, the course and the weather decide what works.