# Half Marathon Pace Calculator

Calculate half marathon pace per mile and km from a target time, or predict your 13.1-mile finish from a 5K or 10K. Includes 5K split times for race day.

## What this calculates

Whether you are targeting a specific half marathon time or wondering what your 5K or 10K fitness translates to over 13.1 miles, this calculator has you covered. Get your required pace and 5K split times to help you pace evenly on race day.

## Inputs

- **Calculation Mode** — options: Target half marathon time to pace, Predict from 5K time, Predict from 10K time
- **Target Half Marathon Time (minutes)** (minutes) — min 50, max 300 — Goal finish time in total minutes (e.g., 105 for 1:45:00)
- **Recent Race Time (minutes)** (minutes) — min 10, max 180 — Your recent 5K or 10K race time in total minutes

## Outputs

- **Half Marathon Finish Time** — formatted as text — Predicted or target half marathon finish time
- **Pace (min/km)** — formatted as text — Required pace per kilometer
- **Pace (min/mile)** — formatted as text — Required pace per mile
- **5K Split Times** — formatted as text — Split times at 5K, 10K, 15K, and 20K marks
- **Average Speed** — Average running speed

## Details

The half marathon (21.0975 km / 13.1 miles) has become the fastest-growing race distance in the world. It demands real endurance training but does not require the months-long buildup of a full marathon, making it an attractive goal for intermediate runners.

Finish times span a wide range. Elite runners complete a half marathon in under 60 minutes, experienced club runners target 1:30 to 1:50, and recreational runners typically finish between 2:00 and 2:30. Your ideal pace depends on your current fitness, training volume, and race experience.

The predictions from shorter race times use the Riegel formula (T2 = T1 x (D2/D1)^1.06), which accounts for the natural pace slowdown as distance increases. Predicting from a 10K is more accurate than from a 5K because the 10K is closer in distance and demands similar aerobic capacity. The formula assumes both races were run at full effort on comparable courses.

Race day pacing is critical for the half marathon. Going out too fast in the first 5K is the most common mistake and leads to a painful final 5K. A conservative approach -- running the first 5K at target pace or slightly slower, settling into rhythm for the middle 10K, and pushing the final 5K if you have energy left -- produces the most consistent results. Use the split times to check yourself at each 5K marker.

## Frequently Asked Questions

**Q: What is a good half marathon time?**

A: For male recreational runners, finishing under 2 hours is a common goal that represents solid fitness. For female recreational runners, under 2:10 is comparable. More experienced runners target sub-1:45 (men) or sub-1:55 (women). Elite times are under 1:00 for men and under 1:06 for women. For a first half marathon, any finish is an accomplishment, and under 2:30 is a respectable debut time.

**Q: How do I predict a half marathon from my 10K time?**

A: Select "Predict from 10K time" and enter your recent 10K time in minutes. The calculator uses the Riegel formula to estimate your half marathon time. As a rough rule of thumb, your half marathon time is typically about 2.22 times your 10K time (slightly more than doubling). A 50-minute 10K runner might predict around 1:51 for the half marathon.

**Q: Should I run negative splits in a half marathon?**

A: A slight negative split (running the second half faster than the first) is the ideal pacing strategy for most runners. Start 5-10 seconds per km slower than goal pace for the first 3-5 km, settle into goal pace for the middle section, and pick up the pace slightly if you feel strong after 15K. This approach prevents the energy crash that comes from starting too fast and often leads to a faster overall time.

**Q: How many weeks should I train for a half marathon?**

A: Most training plans are 10-16 weeks long. If you can already run 5-6 km comfortably, a 12-week plan is typical. If you are starting from minimal running fitness, allow 16-20 weeks. Key elements include one long run per week (building to 18-20 km), midweek tempo or interval sessions, and enough easy running to build weekly mileage gradually. Total weekly volume of 40-55 km per week is common for recreational half marathon runners.

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Source: https://vastcalc.com/calculators/health/half-marathon-pace
Category: Health & Fitness
Last updated: 2026-04-08