Calculate your ideal half marathon pace per mile and per km from a target finish time. Includes mile-by-mile splits, negative-split strategy, and nutrition timing.
The half marathon is the fastest-growing race distance in the world — and it rewards smart pacing. Unlike a 5K where you can push from the gun, or a marathon where glycogen depletion dominates, the half marathon sits in a sweet spot where both speed and endurance matter equally.
This calculator converts your target half marathon finish time into a detailed pacing plan with mile-by-mile (or km-by-km) splits. You can choose even splits, a negative split strategy (faster second half), or customize your approach. It also provides fueling and hydration timing markers based on your projected split times.
Enter your goal time and get a race day blueprint you can wear on your wrist. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process.
A well-paced half marathon means the difference between a PR and a bonk at mile 10. Even a small pacing error of 10 seconds per mile too fast in the first 5 miles can cost you 2–3 minutes by the finish. This calculator ensures you have a plan before the gun goes off.
Pace = Target Time / 13.1094 miles (or / 21.0975 km) For negative splits: • First half pace = Average Pace × (1 + adjustment%) • Second half pace = Average Pace × (1 − adjustment%) Most sub-1:45 runners benefit from 1–2% negative splits.
Result: Pace: 8:00/mi (4:58/km) | 5K split: 24:51 | 10K split: 49:43
A 1:45:00 half marathon requires 8:00/mi or 4:58/km pace. With even splits, you'd pass 5K at 24:51, 10K at 49:43, and 10 miles at 1:20:00. Fueling should happen around miles 4–5 and 8–9.
The half marathon distance (13.1 miles / 21.1 km) is uniquely positioned: long enough to demand endurance but short enough to reward speed. Physiologically, it's run at approximately 80–85% VO₂max for most runners, right at or slightly above the lactate threshold. This makes pacing critical — even small deviations above threshold pace compound rapidly.
Unlike the marathon, most runners can complete a half marathon on pre-race nutrition alone if they're under 1:30. For longer finishers, simple sugars (gels, chews, or sports drink) maintain blood glucose and delay fatigue. The key timing window is 30–45 minutes before you expect to feel the effort increase, typically around miles 4–6.
If you've raced a 10K, you're most of the way to a half marathon. Add 2–4 weeks of long runs (10–14 miles), maintain your tempo work, and you're ready. The half marathon is the ideal stepping stone to the marathon.
Average finish times hover around 2:00–2:10 for men and 2:15–2:25 for women. Sub-1:45 is above average, sub-1:30 is strong, sub-1:20 is advanced, and sub-1:10 is elite. Your target should be based on recent training paces and a 10K race result.
Half marathon pacing is more forgiving — you're unlikely to hit a glycogen wall. You can afford a slightly more aggressive start compared to a marathon. However, going out too fast in the first 3 miles still backfires, with studies showing 15–20 second/mile slowdowns in the final 5K.
Yes. Eat a familiar, carb-rich meal 2–3 hours before the start (300–500 calories). Toast with peanut butter, oatmeal with banana, or a bagel with jam are popular choices. Avoid high-fiber or high-fat foods that may cause GI distress during the race.
If you're finishing in under 1:30, probably not. For 1:30–2:00, one gel at mile 5–6 is helpful. Over 2:00, take a gel at mile 4–5 and another at mile 8–9. Always practice fueling in training first.
A quick estimate: multiply your 10K time by 2.22. So a 50-minute 10K predicts approximately 1:51. For more precision, use the Riegel formula: HM time = 10K time × (21.0975/10)^1.06 = 10K time × 2.2246.
Running the second half faster than the first. A 1–2% negative split means running the first half about 30–90 seconds slower than the second half. This conserves energy early and allows a strong finish. Research shows it correlates with faster overall times.