# Running Split Planner

> Turns one distance and finish time into an even-pace checkpoint sheet. It shows kilometre and mile pace, handles a shortened final split, and downloads every checkpoint as CSV without sending a training target anywhere.

Use it: https://tessalor.com/en/health/running-split-planner

This tool runs entirely in the browser. Nothing entered into it is uploaded.

## Formula

```
totalMetres  = distanceKm x 1,000
totalSeconds = finishMinutes x 60

secondsPerMetre = totalSeconds / totalMetres
pacePerKm       = secondsPerMetre x 1,000
pacePerMile     = secondsPerMetre x 1,609.344

splitCount = ceiling(totalMetres / chosenSplitMetres)

checkpointDistance[n] = min(n x chosenSplitMetres, totalMetres)
checkpointTime[n]     = totalSeconds x checkpointDistance[n] / totalMetres

Every checkpoint uses the unrounded totals. Displayed times are rounded only
after the checkpoint has been calculated.
```

## Assumptions

- The sheet is an even mathematical pace from start to finish. It does not model hills, wind, congestion, aid stations, warm-up, fatigue or a deliberate negative split.
- Distance arrives in kilometres. The measurement-system switch converts miles at the input boundary, so the formula receives one base unit whichever control the visitor sees.
- One international mile is exactly 1,609.344 metres. A track-lap row is 400 metres; a real runner in an outside lane travels farther unless the start is staggered.
- Each displayed clock is rounded independently to the nearest second. Adding those rounded split labels can differ from the exact finish by a few seconds, so cumulative checkpoints come from the unrounded total instead.
- This is a planning aid, not medical or coaching advice. A target can be mathematically consistent and still be unsuitable for a particular runner.

## Inputs

| Name | Label | Type | Default | Range |
| --- | --- | --- | --- | --- |
| `distance` | Race distance | number | 10 | 0.1 to 1000 |
| `finishMinutes` | Target finish time | number | 50 | 0.01 to 14400 |
| `splitUnit` | Split every | select | kilometre |  |

## Outputs

- `pacePerKm` — Pace per kilometre (clock), primary
- `pacePerMile` — Pace per mile (clock)
- `averageSpeed` — Average speed (km/h) (number)
- `splitCount` — Rows in the split sheet (integer)
- `finalSplit` — Final split (number)

## Questions

### What is the difference between pace and speed?

Pace is time per unit of distance, such as 5:00 per kilometre. Speed is distance per unit of time, such as 12 kilometres per hour. They describe the same average from opposite directions: doubling speed halves pace.

### Why is the last row shorter than the others?

The course is not always a whole number of the chosen split. A marathon is about 26.2188 miles, so a mile sheet needs 26 full rows and one final row of about 0.2188 mile to reach the actual finish.

### Why can the displayed split times add to a different total?

Each display is rounded to a whole second. Repeating a rounded label also repeats its rounding error, while the cumulative column is calculated afresh from the requested finish time and therefore lands on it exactly.

### Does the split sheet recommend a safe pace?

No. It only divides a target supplied by the visitor. Fitness, conditions, terrain and health determine whether that target is reasonable; none of those are inferred here.

## Sources

- [SI Units — Length](https://www.nist.gov/pml/owm/si-units-length) — National Institute of Standards and Technology, applies to international mile and exact metric conversion. Retrieved 2026-08-01.
- [Track and Field Facilities Manual 2019 Edition — Chapters 1–3](https://worldathletics.org/responsive/download/downloaddirect?filename=7d39b677-8043-45f4-89f4-6c8814023057.pdf&urlslug=Track%2Band%2BField%2BFacilities%2BManual%2B2019%2BEdition%2B-%2BChapters%2B1-3) — World Athletics, applies to 400 metre standard track. Retrieved 2026-08-01.
- [World Athletics Terms and Abbreviations](https://worldathletics.org/download/download?filename=WA_Terms__Abbreviations_EN+-+July+2023v2.pdf&urlslug=Terms+and+Abbreviations) — World Athletics, applies to marathon distance of 42.195 kilometres. Retrieved 2026-08-01.

## Variants

- [What are the kilometre splits for a 50-minute 10K?](https://tessalor.com/en/health/running-split-planner/10k-in-50-minutes-splits)
- [What mile pace finishes a marathon in four hours?](https://tessalor.com/en/health/running-split-planner/four-hour-marathon-mile-splits)

---

Estimate, not advice. See https://tessalor.com/en/disclaimer.
Machine-readable catalogue: https://tessalor.com/api/tools.json