Splits Calculator
Enter a distance and a finish time to see your splits.
How to use the splits calculator
Enter a goal finish time and a race distance, then choose your unit (km or miles). The table instantly shows the per-segment time you need to hit your target. To go beyond even pace, drag the pacing strategy slider: moving it toward negative splits makes the second half faster; positive splits put more speed into the first half. Your overall finish time stays exactly the same — only the distribution changes.
Why even splits are the default
Running even splits — the same time for every kilometre or mile — is one of the most reliable pacing strategies for most races and most runners. Going out too fast burns fuel and accumulates fatigue faster than your body can clear it. The result is a sharp slowdown late in the race, commonly called a blow-up.
An even-paced race feels conservative in the first half and controlled in the second. Treat the even-splits row as your baseline plan, load it into your GPS watch, and use any deviation as a cue to check your effort.
Negative splits: finishing faster
A negative split means the second half is quicker than the first. For the half marathon and marathon, a modest negative split — five to ten seconds per kilometre faster from halfway — is both practical and effective once you have the discipline to hold back early. Move the slider toward negative to see how each segment reshapes without changing your goal time.
Positive splits: a planning tool, not a target
The positive-split option on the slider is mainly useful for understanding what you are trying to avoid. It shows exactly how expensive an aggressive start is: a few seconds per km too fast in the early kilometres leads to a much steeper slowdown later. Use it to analyse past races where you faded, and to appreciate how small deviations in km 2–5 compound over a full race.
Using splits on race day
Once you have your target splits, print them or save them to your phone. Note the cumulative time at each 5 km mark or major landmark. On race day, check off each point as you pass it — by cumulative time, not just lap time — so you can make real adjustments if conditions change.
Combine this with the pace zones calculator to understand what effort zone your split pace corresponds to in training, and the race time predictor to set a realistic goal in the first place.
For more on pacing strategy and how to choose between even and negative splits, read the splits guide.
How the math works
Two inputs drive everything: your goal finish time and the total race distance. Divide one by the other and you get your average pace — a 1:59:00 half marathon (21.0975 km) averages 5:38 per kilometre. Multiply that average pace by each segment's length (1 km, or one mile if you're on the imperial toggle) and you get the even split for that segment; add the splits up as you go and that's the cumulative time in the third column. If the distance doesn't divide evenly into whole segments — a half marathon is 21 full kilometres plus a 97.5 m tail — the last row is simply shorter, sized to whatever remains.
That's the pacing-strategy slider sitting at 0%: dead-even splits, one number repeated down the whole table.
Moving the slider away from zero layers a second calculation on top, without ever touching the finish time. Every segment gets a small percentage speed adjustment based on where its midpoint falls in the race, expressed as a fraction from 0 (start) to 1 (finish). A segment right at the start gets the largest adjustment; a segment right at the finish gets the same-sized adjustment in the opposite direction; a segment straddling the halfway point gets almost none. Push the slider toward a negative split and every segment before halfway is nudged slower while every segment after halfway is nudged faster — smoothly, not as a sudden switch at the halfway line. Push it toward a positive split and the nudges flip direction: fast early, slow late.
Because those nudges mirror each other around the halfway point, they cancel out over the full distance — adding up all the adjusted splits already lands almost exactly back on your goal time, and the calculator applies a hairline rescale to erase any leftover rounding. The result: whatever bias you dial in, from a barely-there 1% to the maximum ±10% the slider allows, the table always adds up to the exact finish time you typed in — only the shape of the race changes.
Worked example
Say your goal is a sub-2:00 half marathon — 1:59:00 for 21.0975 km — and rather than grinding out even pace the whole way, you want a modest negative split: start controlled, finish strong.
Step 1 — get the even-pace baseline. Enter 21.0975 km and 1:59:00 with the slider at 0%. The calculator divides 7,140 seconds by 21.0975 km and returns a flat 5:38 per kilometre for all 21 full kilometres, plus a 33-second final 97.5 m stretch.
Step 2 — dial in a negative split. Move the slider to 1.5% negative. The calculator recomputes every row: kilometre 1 comes out at 5:41 (three seconds slower than even pace), and the per-km time then eases down, kilometre by kilometre, to 5:36 by kilometre 21 (two seconds faster than even pace) — still finishing in exactly 1:59:00.
Step 3 — check the halves. The first 10.55 km comes home in 59:43; the second half comes home in 59:17 — a 27-second negative split, close to the roughly-30-second swing often used as a rule-of-thumb target for a controlled, not-too-aggressive negative split.
Here's an excerpt of that 1.5%-bias table — first, middle and last full kilometre, plus the finish:
| Km | Split | Cumulative |
|---|---|---|
| 1 | 5:41 | 5:41 |
| 11 | 5:38 | 1:02:16 |
| 21 | 5:36 | 1:58:27 |
| Finish (21.0975) | 0:33 | 1:59:00 |
Enter the same numbers into the splits calculator above and set the slider to 1.5% negative to reproduce every row exactly.
Frequently asked questions
- What are even splits?
- Even splits mean running each segment of the race in the same time, which is often the most efficient way to race.
- Should I run negative splits instead?
- Many runners aim to run the second half slightly faster (negative splits); use these even splits as a baseline.
- What is a positive split?
- A positive split means running the first half faster than the second — usually the result of starting too fast and fading. Drag the slider toward a positive split to see how it reshapes your per-km times, then plan to avoid it on race day.
- What are splits in running?
- A split is your time for one segment of a race — usually each kilometre or mile. Lined up in order, your splits show the shape of your effort across the whole race: flat, rising, or falling.
- How do I decide between even and negative splits?
- If you are new to a distance or unsure of your fitness, start with even splits — they are the simplest plan to execute and the hardest to get badly wrong. Once you can hold back early in training without it feeling unbearable, try a modest negative split (a few seconds per km) for extra finishing speed.
- How do I use splits during a race?
- Note the cumulative time at each kilometre or 5K mark, not just the split for that segment alone, so a single slow or fast patch does not throw off your read on the whole race. Check your watch against that cumulative target at each checkpoint and adjust effort — not just pace — if you are drifting off plan.
- What is a good 5K split strategy?
- Even splits are the safest default for a 5K: the race is short enough that a fast start you cannot sustain shows up almost immediately as a painful fade. A slight negative split — a few seconds per km faster in the last mile once you know the finish is close — works well for experienced 5K runners, but keep the bias modest and treat even pace as the baseline.