Negative Split Calculator
Choose the race distance, goal time and the number of seconds the second half should be faster. A negative number gives a positive split instead. Use it to plan a negative split for a 10K, half marathon or marathon.
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Formula
With total time T and a difference d (seconds the second half is faster):
first half = (T + d) / 2second half = (T - d) / 2pace per half = half time / (distance / 2)
A negative d gives a positive split (slower second half). 1 mile = 1.609344 km.
Worked example
10 miles in 1:30:00 (5,400 s), second half 60 s faster.
- First half: (5,400 + 60) / 2 = 2,730 s = 0:45:30, which is 9:06 per mile.
- Second half: (5,400 - 60) / 2 = 2,670 s = 0:44:30, which is 8:54 per mile.
- Even pace would be 5,400 / 10 = 540 s = 9:00 per mile.
When to use it
Use it when you want to start conservatively and finish faster. Enter the distance, goal time and the number of seconds the second half should be quicker, and you get both half times and the pace for each. Enter a negative difference to see what a positive split (fading) would look like.
Typical values (rules of thumb)
- A negative split of a few tens of seconds up to a couple of minutes is common for a 10K to a marathon.
- Elite marathon records have often been run with nearly even halves, so an extreme target is not required.
Common mistakes
- Starting the first half too slow and then running the second half out of reach. Keep the target realistic.
- Forgetting that hills and wind change the real pace. Use the plan as a guide and run by effort.
- Mixing up the sign: a positive difference here means the second half is faster.
How it differs from nearby tools
The marathon pace calculator gives an even pace and 5 km splits, and the split time calculator shows each km or mile. This page owns the half-by-half plan.
Frequently asked questions
What is a negative split?
It is running the second half of a race faster than the first. Many distance coaches suggest it because starting too fast often leads to a late slowdown.
How are the half times calculated?
First half = (total + difference) ÷ 2 and second half = (total − difference) ÷ 2. For 10 miles in 1:30:00 with a 60 second difference: (5,400 + 60) ÷ 2 = 2,730 s (45:30) and 2,670 s (44:30).
What paces does that give?
Divide each half time by half the distance. In the 10 mile example each half is 5 miles: 2,730 ÷ 5 = 546 s, or 9:06 per mile, then 2,670 ÷ 5 = 534 s, or 8:54 per mile. The even pace is 9:00.
How big should my split difference be?
Small is safer. A difference of 1 to 2 percent of the total time is a common starting point; for a 4:00:00 marathon that is 2 to 5 minutes. This calculator only does the arithmetic, so choose a value that suits your fitness and the course.
What is a positive split?
A positive split means the second half is slower than the first. Enter a negative difference: a 4:00:00 marathon with -120 s gives a first half of 1:59:00 and a second half of 2:01:00.
How do you calculate a negative split for a half marathon?
First half = (goal time + difference) / 2 and second half = (goal time - difference) / 2. For a 1:45:00 half marathon with a 60 second difference, the halves are 53:00 and 52:00, about 5:01 and 4:56 per km.
Is a negative split faster than even pacing?
Not necessarily. The goal time is the same in this calculator, so a negative split only changes how the effort is spread. Many runners find it reduces the risk of fading, but an even pace can be just as fast.