What this Half Marathon Pace Calculator does
This English-language half marathon pace calculator takes your goal finish time — or a recent race result — and returns your required pace per kilometer and per mile, a full split table, and a Riegel-formula time prediction. Whether you're chasing a 2hr half marathon pace or dialing in a conservative first-race target, the numbers update instantly. 100% client-side — your data never leaves your browser. No uploads, no tracking, no server logs. If you're also monitoring body composition alongside your training load, our [Calories Burned Calculator](/en/calories-burned-calculator/) covers energy expenditure for long runs.
Features
- Pace per km and mile. Enter a goal time and distance; get back pace in both metric and imperial units simultaneously — no extra steps.
- Half marathon split calculator. Generates a full split table for every kilometer and every mile marker so you can print or screenshot your race-day pacing band.
- Riegel race predictor. Paste a recent 5K or 10K result and the Riegel formula projects your half marathon finish time, giving you a data-grounded target instead of a guess.
- Half marathon pace chart. Visual pace chart spanning common finish-time targets from 1:30 to 3:00, so you can compare your goal against the broader half marathon pace chart landscape.
- Negative-split mode. Toggle a negative-split strategy to see first-half and second-half paces side by side — useful for courses with elevation changes like Austin's 3M Half.
- Privacy by design. No account, no cookies, no telemetry. The entire calculation runs in JavaScript inside your browser tab. Close the tab and nothing persists.
How to use the Half Marathon Pace Calculator
Three inputs are all you need: a distance (half marathon is fixed at 21.0975 km), a goal time, and optionally a recent race result for prediction.
- Enter your goal finish time. Type your target time in
HH:MM:SSformat — for example1:55:00for a sub-2-hour attempt. - Review pace and splits. The calculator immediately shows pace per km, pace per mile, and a complete split table. You can copy the table with the Copy button.
- Run the Riegel predictor (optional). Enter a recent 5K or 10K result and the tool estimates your half marathon finish time using the industry-standard Riegel formula.
- Toggle units or split strategy. Switch between km/mile display or enable negative-split mode to see asymmetric pacing across both halves of the race.
Common use cases
- First-time half marathoner. A runner in San Francisco training for their first race uses the half marathon time calculator to convert a comfortable 10K result into a realistic half marathon finish time predictor, then prints the split chart for race day.
- Targeting a round-number milestone. Runners chasing exactly 2:00:00 use the 2hr half marathon pace output — 5:41/km or 9:09/mile — to set treadmill and GPS watch targets weeks before the event.
- Coach building a training plan. A running coach enters multiple athletes' 10K PRs into the half marathon race predictor and exports the split tables to share personalized pacing bands for an upcoming team race.
- Race-day pacer. A pace group leader uses the half marathon pacer split table to keep a group on even effort across both halves of a hilly course, adjusting at each mile marker.
- Cross-training athlete. A triathlete tracking overall fitness pairs this tool with the [TDEE calculator](/en/tdee-calculator/) to align running pace targets with their weekly calorie and energy output goals.
Frequently asked questions
Does this calculator store or upload my times anywhere?
No. Every calculation runs entirely inside your browser using JavaScript. Nothing is sent to any server, logged, or stored after you close the tab. There are no accounts or cookies involved.
How accurate is the Riegel race predictor?
The Riegel formula (T2 = T1 × (D2/D1)^1.06) is widely used and reasonably accurate for trained runners on similar courses. It tends to overestimate finish times slightly for very fit athletes and underestimate them for runners who haven't built half-marathon-specific endurance. Use it as a starting bracket, not a guarantee.
What pace do I need to run a 2-hour half marathon?
A 2:00:00 half marathon requires an average pace of 5:41 per kilometer or 9:09 per mile. Held perfectly even across all 21.0975 km, that's 11 seconds per km slower than a 5:30/km 10K effort — achievable but demanding aerobic discipline.
Can I use a 5K time to estimate my half marathon finish time?
Yes. Enter your 5K result in the predictor section and the Riegel formula scales it to a half marathon projection. Keep in mind that half-marathon-specific long runs and tempo work will shift actual performance closer to — or better than — the prediction.
What is a half marathon pace chart?
A half marathon pace chart maps common goal finish times (typically 1:30 through 3:00) to their corresponding per-kilometer and per-mile paces, plus splits at each marker. This calculator generates a personalized chart for any target you enter, so you're not limited to round-number rows in a static table.
How is this different from a generic pace converter?
A half marathon pace converter only converts between time-per-km and time-per-mile. This tool adds a full split table, a Riegel finish-time predictor based on shorter race results, and optional negative-split modeling — giving you race-ready numbers rather than just a unit conversion. Accurate input handling matters: as the Adolphe Quetelet (Britannica) legacy in body metrics shows, small formula errors at scale produce misleading outputs. The same principle applies here — we validate every input before computing. See also the OWASP — Password Storage Cheat Sheet philosophy: defaults should be safe, and no user data should be processed server-side unnecessarily.