Half-by-half split calculator
Choose how your target time is shared between two equal distances.
Plan settings42.195 km · 4:00:00Edit
Even pace · 42.195 km
Pace for each half
Above 50% gives more time to the first half, so the second half is faster. This is a mathematical plan.
Cumulative splits
Markers: 10, including the finish.
| Marker | Elapsed time | Segment time |
|---|---|---|
| 5 km | 0:28:26 | 28:26 |
| 10 km | 0:56:53 | 28:26 |
| 15 km | 1:25:19 | 28:26 |
| 20 km | 1:53:45 | 28:26 |
| Half · 21.0975 km | 2:00:00 | 6:15 |
| 25 km | 2:22:12 | 22:12 |
| 30 km | 2:50:38 | 28:26 |
| 35 km | 3:19:05 | 28:26 |
| 40 km | 3:47:31 | 28:26 |
| Finish · 42.195 km | 4:00:00 | 12:29 |
Times rounded independently to the nearest second.
Use this result with confidence
Allocate your chosen total time between equal distance halves and check both half times and paces.
Choose how much time belongs to the first half
The control sets the first half’s share of your total time. At 50%, both halves take the same time. Above 50%, the first half takes longer and the second half is faster. Below 50%, the first half is faster. The available range is 45% to 55%.
A 51% / 49% four-hour example
For a four-hour marathon, 51% of 14,400 seconds is 7,344 seconds: 2:02:24. The second half uses the remaining 7,056 seconds: 1:57:36. Each half covers 21.0975 km, so the corresponding displayed paces are about 5:48/km and 5:34/km.
| Part | Time share | Duration | Displayed pace |
|---|---|---|---|
| First 21.0975 km | 51% | 2:02:24 | 5:48/km |
| Second 21.0975 km | 49% | 1:57:36 | 5:34/km |
| Full 42.195 km | 100% | 4:00:00 | 5:41/km overall |
Read the halfway transition
Within each half, cumulative times use that half’s constant pace. A segment that crosses halfway includes time at both rates. The second-half time is calculated as the total minus the first-half time so the two parts preserve the exact target.
Common questions
What makes a split negative?
The second half takes less time than the first over the same distance. Choose Custom split and set the first-half time share above 50%. At 51%, a two-hour half marathon splits into 1:01:12 and 0:58:48, a difference of 2:24.
Does 51% mean running the second half 1% faster?
It assigns 51% of your total time to the first half and 49% to the second. It is a share of time, rather than a percentage change in speed. The calculator holds one constant pace within each half; it does not gradually accelerate through the race.