Split times calculator
Your pace per kilometre and your split times, every km or every 5 km, for a 10K, a half or a marathon, with your pace and speed.
Updated 30 September 2026
A 3:30 marathon goal is not run with a finishing time in mind but with a pace: 4:59 per kilometre, 1:45 at halfway. This calculator turns your goal time into markers you can check at every kilometre sign.
The classic race-day trap is starting too fast, carried by the crowd and fresh legs. Having your split times in front of you, noted down or memorised at the key points, shows by the 5th kilometre whether you are ahead — and lets you ease off while it still costs nothing.
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How it is computed
Pace is the goal time divided by the distance: 3:30, or 12,600 seconds, divided by 42.195 km gives 298.6 seconds, that is 4:59 per kilometre. Speed is the reverse: 42.195 km in 3.5 hours is 12.06 km/h.
Each split is that pace multiplied by the distance covered. The calculation uses the exact pace, not the pace rounded to the second: at exactly 4:59 the same marathon would end in 3:30:16. Sixteen seconds is the difference between breaking the barrier or not.
The splits assume an even pace from start to finish, with no cautious start or final push built in. The halfway split is always shown, even when it does not fall on a round kilometre (10.55 km on a half), and so is the finish.
The plans built from this number
Now the plan that goes with it
These numbers are exactly the ones Endu uses to build a full preparation: phases, volume, detailed sessions, exported to your watch. 14-day trial, cancel any time.
Create my planFrequently asked questions
- Why does my watch beep before the kilometre signs?
- Official courses are measured along the shortest line, cutting every corner. In a race you weave, overtake and go round aid stations: you always run a little more than the stated distance, and GPS adds its own error. Trust the signs rather than the pace on your watch, and keep a few seconds in hand.
- Should I start slower and finish faster?
- A first half slightly slower than the second — a “negative split” — is a common strategy, but the gap should stay small: a few seconds per kilometre. For an amateur runner, even pacing is already a demanding goal: the most frequent mistake is still to start too fast and slow down in the second half. That is why this calculator only offers even pacing.
- Every kilometre or every 5 km?
- On a half or a marathon, splits every 5 km are enough to know where you stand and are easier to remember. Kilometre splits help on 5K and 10K, where a few seconds too fast early on are paid for quickly.