Half Marathon Pace Calculator With Splits

This half marathon pace calculator works out the average pace needed to finish 13.1 miles (21.0975 km) in your target time, then gives the equivalent speed. Enter your finish time and distance; use the pace result to plan even splits or adjust your goal.

Formula

Average pace (minutes per kilometre) = finish time in minutes ÷ distance in kilometres. The calculator then finds average speed as distance ÷ time in hours.

• t is the finish time, entered in minutes.
• d is the distance, entered in kilometres.
• pace is the average time per kilometre, in min/km.
• speed is the average distance per hour, in km/h.

For a half marathon, the standard race distance is 21.0975 km, approximately 13.1094 miles. To calculate pace in minutes per mile instead, divide the total time in minutes by 13.1094, or use the rounded 13.1-mile distance for a practical estimate. Keep the time and distance units consistent.

Worked Example

Using the calculator defaults, a finish time of 120 minutes and a distance of 21.0975 km:

1. Pace = 120 ÷ 21.0975 = 5.6879 minutes per kilometre.
2. Convert the decimal fraction to seconds: 0.6879 × 60 = 41.27 seconds. Rounded to two decimals, the pace is 5.69 min/km, or about 5 minutes 41 seconds per kilometre.
3. Speed = 21.0975 ÷ (120 ÷ 60) = 10.54875 km/h, which rounds to 10.55 km/h.

The pace is an average across the full distance. At the unrounded pace, a runner would cover each kilometre in about 5:41.3; multiplying that exact pace by the full distance returns 120 minutes. Display rounding can make a hand-calculated total differ by a few seconds.

Half Marathon Splits at Your Target Pace

A split is the time taken to cover a particular section of the course. For an even-pace plan, multiply the target pace by each distance marker. Using the example above, the unrounded pace is about 5:41.3 per kilometre. Approximate cumulative targets are:

• 5 km: 28:26
• 10 km: 56:53
• 15 km: 1:25:19
• 20 km: 1:53:46
• Finish at 21.0975 km: 2:00:00

These are elapsed times from the start, not the duration of each split. For instance, the 10 km split means you should reach 10 km about 56 minutes 53 seconds after starting. A race may mark miles rather than kilometres: at the same goal, one mile takes about 9:09, and 13.1 miles takes roughly two hours. Small differences can arise because 13.1 miles is a rounded version of the official metric distance.

To calculate an individual segment, subtract the elapsed time at its starting marker from the time at its ending marker. A pace chart is a guide, not a promise that every kilometre will take exactly the same time. Turns, hills, crowding, and the precise placement of course markers can affect recorded splits.

How to Choose a Target Time

Start with a goal that is realistic for your current running, not just a pace that looks appealing on a chart. A target time is useful only if you can sustain its required average across the full race. If you have recent race results or training data, compare them with the pace implied by your goal and account for the half marathon’s route and conditions.

For reference, common target times correspond approximately to these average paces over 21.0975 km:

• 1:30:00: 4:16 per km (about 6:52 per mile)
• 1:45:00: 4:59 per km (about 8:01 per mile)
• 2:00:00: 5:41 per km (about 9:09 per mile)
• 2:15:00: 6:24 per km (about 10:18 per mile)

Each pace is rounded to the nearest second, so multiplying the displayed pace by the full distance may not reproduce the target time exactly. Use the finish-time calculation as the reference and treat rounded pace charts as practical guides.

Using Splits in a Race Plan

Even pacing means aiming for a similar effort and pace throughout, but it does not always mean identical watch readings at every marker. GPS distance can drift, mile and kilometre signs may not align precisely with the watch, and a course’s elevation changes the effort required. A sensible plan uses official course markers as well as the watch, rather than reacting sharply to every momentary pace fluctuation.

Some runners plan a slightly slower opening section and a stronger finish; others aim for even splits. A faster second half is often called a negative split. Either strategy changes the segment targets while leaving the overall target time unchanged. If you create a varied plan, make sure the segment durations add up to your goal. Avoid making up for a slow kilometre with an abrupt surge based only on a small GPS discrepancy.

Common Errors and Calculator Limits

• Entering hours as minutes: Convert first. A two-hour target is 120 minutes, not 2.
• Mixing miles and kilometres: This calculator expects kilometres. If you enter 13.1 as the distance, the pace is interpreted as minutes per kilometre, not minutes per mile. Convert the distance or calculate in the matching unit.
• Confusing pace and speed: A lower min/km value means a faster pace; a higher km/h value means a faster speed.
• Rounding too early: Keep extra decimal places while calculating cumulative splits, then round the displayed times to seconds.
• Assuming average pace guarantees a result: The calculation describes the pace required for a time. It cannot account for race-day conditions, course measurement, stops, or how a runner performs.

The calculator gives an arithmetic average, not a personalized prediction or a complete race plan. It also does not account for elapsed time lost at aid stations or other pauses. If your goal refers to official finish time, make clear whether your split plan includes those pauses.

Frequently Asked Questions

What pace per kilometre is a two-hour half marathon?
A 2:00:00 finish over 21.0975 km requires an average of about 5:41.3 per kilometre, commonly shown as 5:41/km. The rounded figure is not exact enough to reproduce the finish time on its own.

What pace per mile is a two-hour half marathon?
Using the standard distance of about 13.1094 miles, the average is about 9:09 per mile. If you use 13.1 miles as a rounded distance, the estimate differs slightly.

How do I calculate a half marathon split?
For an even pace, multiply your unrounded pace by the distance marker to get cumulative elapsed time. To find the time for one segment, subtract the cumulative time at its start from the cumulative time at its end.

Should half marathon splits be even?
Not necessarily. Even splits are a simple planning baseline, while a controlled slower opening or a faster second half may suit a particular course or runner. Whatever pattern you choose, check that all segment times sum to the target finish time.

Why does my watch show a different pace from the course markers?
GPS estimates can differ from measured course distance, especially around turns or where satellite reception is limited. Watches may also record a distance slightly longer than the marked race route. Use official markers for cumulative race splits and treat instantaneous GPS pace as an estimate.

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in t | Finish time | min | 120 | 0
in d | Distance | km | 21.0975 | 0
out pace | Average pace | min/km | t / d | 2
out speed | Average speed | km/h | d / (t / 60) | 2