Marathon splits calculator: even and negative splits

Type in your goal finish time and this marathon splits calculator gives you the split and the elapsed time for every mile (or every kilometer) of the race, at even pace or with a 1%, 2% or 3% negative split. It starts at 4:00:00; change it to your own goal.

Even splits vs negative splits

A split is your time for one section of the race, or your total time when you reach a marker.

• Even splits mean the same pace from start to finish. For a 4:00 marathon that's 9:09 per mile, every mile.
• Negative splits mean the second half is faster than the first. You start a little slower than goal pace and finish a little faster.
• Positive splits mean you slow down in the second half. On average, this is what marathoners do, usually not on purpose. A study of about 92,000 performances in 14 US marathons found runners were on average 15.6% (men) and 11.7% (women) slower over the second half (Deaner et al., 2015).

Which works best? In Barry Smyth's analysis of Chicago Marathon results from 2005 to 2016, reported by World Athletics, even splitters (less than 2% difference between halves) averaged 242 minutes, negative splitters 256 and positive splitters 280. Runners whose first 5K was their slowest never hit the wall. Smyth cautions that correlation is not causation: forcing an even split won't guarantee a faster time. Still, the pattern is consistent. Don't start fast, and aim for close to even pace.

Example: a 4:00 marathon, even vs negative split

Here's the same 4:00:00 goal run two ways. The negative split version runs the first half in 2:01:00 (9:14 per mile) and the second in 1:59:00 (9:05 per mile), a gap of only 9 seconds per mile. That's a negative split of about 0.8%; the calculator's 1% option is a touch bigger (2:01:12, then 1:58:48).

The negative split runner is a full minute behind at halfway and catches up over the second half. That takes nerve: when the even-pace runner is ahead of you at 20K, it feels like you're losing. The idea is to have more left for the last 10K, where most runners slow down.

Keep the gap small. A minute or two over 26.2 miles is only a few seconds per mile; a much bigger gap can mean you held back more than you needed to early on.

Mile splits for an even 4:00 marathon

If your race marks miles, these are the clock times to look for:

For other goal times, the marathon pace chart gives the pace for every finish from 2:30 to 7:00.

How to use your splits on race day

Pace band

A pace band is a strip of paper or tape around your wrist with your target time at each marker. Copy five or six checkpoints from the calculator (every 5K or every few miles, plus halfway) rather than all 26 miles, so it stays readable when you're tired. Write it in large print, cover it with clear tape, and add it to your marathon packing list.

Watch

GPS watches are great for steady effort mile to mile, but don't trust the average pace alone. Certified courses are measured along the shortest possible route, plus a tenth of a percent so they're never short, according to a Running USA article by course measurer Doug Thurston. Few runners hold that line exactly, and the same article notes that GPS watches almost always overestimate race distance by at least 1%.

Here's what that does. Say your watch reads 26.5 miles at the finish, about 1% long. If you held its 9:09 per mile all day, you'd finish in 4:02:28. To break 4 hours over 26.5 watch miles, its average would have to show 9:03. The fix: compare the race clock time (or your watch's elapsed time) with your pace band at each official marker.

When you're off pace

• A few seconds ahead or behind: do nothing. Hills, water stops and crowding even out.
• More than a minute ahead early on: ease off gradually over the next few miles. Don't stop or walk to "give it back".
• Behind in the second half: don't chase the whole deficit in one mile. Pick up the pace a little and reassess at the next marker.

Plans to go with your splits

Splits only work if your training supports them. If you're aiming for 4:00, the sub 4 hour marathon plan is built for that goal. For other goals, start with the 16 week marathon training plan.