Calculator Inputs
Use target finish mode or pace mode for race planning.
Example Data Table
Sample planning values for a realistic race target.
| Mode | Target / Pace | Stops | Course | Fatigue | Buffer | Strategy | Adjusted Pace | Projected Finish |
|---|---|---|---|---|---|---|---|---|
| Finish to pace | 01:45:00 | 45 sec | +3 sec/km | +2 sec/km | 2 sec/km | Negative split | 4:59 /km | 01:46:03 |
| Pace to finish | 8:00 /mile | 30 sec | +1 sec/km | +2 sec/km | 1 sec/km | Even pacing | 8:02 /mile | 01:45:45 |
Formula Used
Neutral pace per kilometer = (target finish time - planned stop time) ÷ 21.0975, or converted from your entered mile pace.
Adjusted pace per kilometer = neutral pace + course adjustment + fatigue allowance - goal buffer.
Projected finish time = adjusted pace × 21.0975 + planned stop time.
Speed = 3600 ÷ adjusted pace in seconds per kilometer. Mile pace is adjusted kilometer pace × 1.609344.
Split strategy uses weighted multipliers across race segments. The tool normalizes them so segment pacing changes still preserve your overall average pace.
How to Use This Calculator
- Choose whether you want to start from a finish goal or a known pace.
- Enter your time or pace values, then select the preferred pace unit.
- Add stop time if you expect aid station pauses or bathroom breaks.
- Use course adjustment for hills, weather, or difficult surfaces.
- Use fatigue allowance when you expect late-race slowing.
- Use goal buffer if you want a slightly faster working pace.
- Select a split strategy to model even, negative, conservative, or fast-start pacing.
- Press the button to see your summary, split table, and export options.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates neutral pace, adjusted pace, projected finish time, speed, and segment splits for a half marathon using your time goal or current pace.
2. Why is the race distance fixed?
A half marathon has a standard race distance of 21.0975 kilometers, or 13.1094 miles. Fixing the distance keeps the pacing math accurate.
3. What is course adjustment?
Course adjustment adds or subtracts seconds per kilometer to reflect hills, heat, wind, trail surfaces, or any factor that changes real race difficulty.
4. What is fatigue allowance?
Fatigue allowance adds pacing cushion for likely late-race slowdown. It helps produce more realistic pacing targets when endurance fades after early kilometers.
5. What does goal buffer mean?
Goal buffer subtracts seconds per kilometer from the adjusted pace. Use it when you want a slightly quicker working target than the neutral pace.
6. Which split strategy should I choose?
Even pacing suits stable efforts. Negative split fits disciplined racers. Conservative start helps crowded races. Positive split models aggressive early pacing.
7. Can I use mile pace instead of kilometer pace?
Yes. Enter pace mode and switch the pace unit to miles. The calculator converts your pace automatically and shows both kilometer and mile outputs.
8. Do the exports include split rows?
Yes. The CSV and PDF downloads include the main result metrics and the segment split table shown on the page.