Calculate your half marathon pace per km or per mile from a goal finish time, or your finish time from a pace, with 5K and mile checkpoint splits.
How the Half Marathon Pace Calculator Works
The calculator keeps the certified half-marathon distance of 21,097.5 meters throughout the arithmetic, so the final 1.0975-kilometer segment is never lost to a rounded 21.1-kilometer shortcut.
Finish-time mode divides the entered duration by the exact distance. Pace mode converts the selected kilometer or mile pace to seconds per meter and multiplies by 21,097.5.
Half-Marathon Pace and Finish Formula
Formula: pace = finish time / 21,097.5 m; finish time = pace per meter x 21,097.5 m
Every cumulative checkpoint is computed from its exact fraction of the full distance. Display rounding does not accumulate from one row to the next.
Choosing the Right Inputs
Choose the quantity to solve, enter the visible finish-time or pace fields (including zeros), and select a primary display unit. The optional checkpoint selector changes the supporting split rows. The combined plan lists 5K checkpoints followed by selected miles as independent cumulative targets, so segment times are omitted there. Supported finishes are 45 minutes to 8 hours; entered pace must be 2:00 to 30:00 per selected unit.
| Checkpoint | Cumulative time | Segment time | Average pace |
|---|---|---|---|
| 5K | 24:53 | 24:53 | 4:59/km |
| 10K | 49:46 | 24:53 | 4:59/km |
| 15K | 1:14:39 | 24:53 | 4:59/km |
| 20K | 1:39:32 | 24:53 | 4:59/km |
| Finish | 1:45:00 | 5:28 | 4:59/km |
Understanding Your Results
The requested pace or finish time appears first. Equivalent kilometer and mile paces, speed, halfway time, and the selected cumulative checkpoint plan follow.
Use the rows as average targets. They do not require every kilometer or mile to be identical on a real course.
Worked Example
A 1:45:00 finish equals about 4:59 per kilometer and 8:01 per mile. At that average, 10K is reached in about 49:46.
Common Mistakes
Do not calculate with 21.1 kilometers, add rounded interval splits, or treat an average pace as a guarantee on hills, turns, or aid-station sections.
Assumptions and Limitations
The calculator models steady average pace only. It does not adjust for course profile, weather, crowding, stops, or a planned negative split.
Sources
NIST: international mile conversion (1,609.344 m).
World Athletics: half-marathon distance (21.0975 km).
