Even and Negative Split Arithmetic
Understand a first-half time percentage and calculate two exact half times from one target.
Split the distance into equal halves
This calculation divides the distance at its midpoint. The halves have equal length but can receive different amounts of time. A four-hour marathon has two 21.0975 km halves. With a 50% first-half time share, each half takes 2:00:00.
Read the percentage as a share of time
A 51% first-half setting means that 51% of the total duration is assigned to the first half. The remaining 49% belongs to the second half. Because the halves have equal distance, more time for the first half means a slower first half and a faster second half.
| First-half share | First-half time | Second-half time | Meaning |
|---|---|---|---|
| 49% | 1:57:36 | 2:02:24 | First half faster |
| 50% | 2:00:00 | 2:00:00 | Equal half times |
| 51% | 2:02:24 | 1:57:36 | Second half faster |
Calculate each half’s pace separately
At 51%, divide 7,344 seconds by 21.0975 km for the first half, and 7,056 seconds by the same distance for the second. These are about 5:48/km and 5:34/km when rounded. The overall average still describes 4:00:00 across 42.195 km.
Markers use the appropriate half
A marker before halfway uses the first-half rate. A marker after halfway includes the full first-half time plus the second-half time for the distance since halfway. If a regular segment crosses the midpoint, its time contains portions at both rates.