Splits for your race
Your target time shared out kilometre by kilometre. With the option to plan a negative split, which is how the good races get run.
Your figures
Result
- For a target of
- 50:00
- Average pace, first half
- 5:00 /km
- Average pace, second half
- 5:00 /km
- Difference between halves (s/km)
- 0
- Halfway split
- 25:00
Splits, kilometre by kilometre
| Km | Pace | Split | Elapsed |
|---|---|---|---|
| 1 | 5:00 | 5:00 | 5:00 |
| 2 | 5:00 | 5:00 | 10:00 |
| 3 | 5:00 | 5:00 | 15:00 |
| 4 | 5:00 | 5:00 | 20:00 |
| 5 | 5:00 | 5:00 | 25:00 |
| 6 | 5:00 | 5:00 | 30:00 |
| 7 | 5:00 | 5:00 | 35:00 |
| 8 | 5:00 | 5:00 | 40:00 |
| 9 | 5:00 | 5:00 | 45:00 |
| 10 | 5:00 | 5:00 | 50:00 |
What we assume
- The pace change is linear and symmetrical: it shifts progressively from the first kilometre to the last, so the total time is the same whichever strategy you pick.
- Elevation is ignored. On a hilly course, run by effort rather than by pace.
- So are heat, wind and aid stations, which over a marathon can cost real minutes.
How it is calculated
The target time is shared out across the kilometres. Pick anything other than even pacing and the pace shifts progressively: the percentage is the gap between the first and the last kilometre, spread linearly across the race.
Because the adjustment is symmetrical, the average holds and the finish time is identical under all three strategies. What changes is how you arrive.
Why negative splits
Almost every distance record has been run with a faster second half. Going out too fast burns through glycogen early and the cost arrives later, magnified. Starting three or four percent slower than target feels almost lazy for the first few kilometres and buys you the end of the race.
An example
A 10K in 50:00 is 5:00 per kilometre even. With a 4% negative split you would start at about 5:06 and finish at about 4:54: the same 50 minutes, arrived at from the right direction.
Frequently asked questions
Does the strategy change my finish time?
Not in this table: the adjustment is symmetrical, so the average pace and the total are identical. In a real race it very much does, because going out too fast costs more than it gains.
How big should the variation be?
Between 2% and 5% is a sensible negative split. Beyond that you are leaving too much on the table in the first half.
What about hills?
Ignore the per-kilometre pace on a hilly course and run by effort. Chasing a split up a climb is the most reliable way to ruin the last third.
Keep calculating
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