A half marathon is 21.0975 kilometers, half of the marathon’s 42.195 km. In miles that is 13.109, which signs often round to 13.1. The finish time is that distance times your average pace, not “a 10K plus a bit.”
Times at even pace
| Finish | min/km | min/mile |
|---|---|---|
| 1:30:00 | 4:16 | 6:52 |
| 1:45:00 | 4:59 | 8:01 |
| 1:50:00 | 5:13 | 8:23 |
| 2:00:00 | 5:41 | 9:09 |
| 2:15:00 | 6:24 | 10:18 |
| 2:30:00 | 7:07 | 11:27 |
A 2:00:00 half is the same average pace as a 4:00:00 marathon, 5:41/km. Holding it for 13.1 miles does not mean you can hold it for 26.2. The half marathon pace calculator prints 5K checkpoints for the time you type. The marathon pace calculator is the longer course, with its own splits.
Checkpoints inside 2:00:00
At 5:41/km the markers fall on:
- 5K: 28:26
- 10K: 56:53
- 15K: 1:25:19
- 20K: 1:53:45
- Finish (21.0975 km): 2:00:00
The last piece after 20K is 1.0975 km, about 6:15 at that pace, not another full 5K. People who “add five minutes for the last bit” are using a rule of thumb. The table is the arithmetic.
From a 10K or toward a marathon
A recent 10K is a better input than a wish. Put it in the race time predictor and read the half marathon line as an equivalent, then decide if your long run is close enough to trust it. Doubling a half marathon time to plan a full marathon ignores the extra fatigue. How long a marathon takes lists those finish times on their own.
If you only have a pace and no race yet, multiply minutes per kilometer by 21.0975. At 6:00/km that is 2:06:35. The pace calculator does the same multiplication for a custom distance. Average half marathon times by age are wide planning bands around these clocks, not a result you are supposed to match.