Half marathon pace:
the split you need for your goal finish time

From a goal time to a pace per kilometre

A half marathon is exactly 21.0975 kilometres, or 13.1094 miles. Pace is simply how long you take for each of those units, so once you have a goal finish time the rest is a division. The only trap is the unit: pace is quoted in minutes and seconds per kilometre, while the finish time is in hours, minutes and seconds.

The easiest way to avoid mistakes is to convert the finish time to total seconds first. One hour is 3,600 seconds and one minute is 60, so 1 hour 45 minutes is 6,300 seconds. Divide that by the race distance and you have seconds per kilometre, which you then split into minutes and seconds.

Worked example: a 1 hour 45 minute goal

Suppose your target is 1:45:00. Convert the time, divide, and then turn the decimal seconds back into a clock reading.

In speed terms this is about 12.06 km/h. Rounding matters here: running a steady 4:59 for the entire distance gives 1:45:08, eight seconds over the goal. Aim for 4:58 on the watch and you are comfortably inside 1:45:00.

Checkpoints are useful in the race itself. At 5 km you want to be near 24:53 and at 10 km near 49:46. If your watch reads much earlier than that, you are running faster than the plan.

Reference table for common goal times

Notice the spacing: each additional 15 minutes of finish time adds roughly 43 seconds to every kilometre. That gives you a quick mental check. If your pace sits halfway between two rows, so will your finish time.

Even splits, negative splits and the course profile

A flat, evenly paced race is the most efficient way to use your energy, but real courses are rarely flat or perfectly smooth. Many runners aim for an even pace through the first 15 km and then adjust by feel, or deliberately start a few seconds per kilometre slower and finish faster, which is called a negative split.

As an illustration, suppose you want 1:45:00 and plan to run the first half of the course (10.55 km) at 5:03 per km. That takes 3,196 seconds. The remaining 10.55 km must then be run in 3,104 seconds, which is 4:54 per km. The plan works, but only if the final half is within your reach on the day.

• Hills: add 10 to 20 seconds per km on climbs and bank part of it back on the downhill, rather than chasing a flat pace on the watch.
• Crowded starts: the first kilometre is often 10 to 20 seconds slow, so do not panic and sprint to make it up.
• Heat and wind: slow the target pace by 3 to 5 seconds per km as a starting point and treat the finish time as flexible.

What your watch will show against the plan

GPS watches measure the path you actually ran, not the shortest course line. Weaving between runners or cutting corners poorly can add 100 to 300 metres over 21 km, so your watch may show 21.3 km when the finish arch appears. The official time still counts from the timing mats.

It is best to rely on the course's kilometre markers for checking your pace, and use the watch's average pace as a trend rather than a verdict. If the two disagree, trust the markers and the clock.

Using race pace to set training paces

Once you have your target pace, the same figure helps shape your weekly running. Coaches commonly set easy runs well below goal pace, often by about a minute per kilometre, so that most of the mileage stays comfortable. Tempo efforts sit at or slightly faster than half marathon pace, and short intervals run faster still. These ranges vary between plans, so treat them as starting points and follow the plan you are using.

A practical routine is to run a few kilometres of the long run at goal pace in the second half of the session, when your legs are tired. That rehearses how 4:59 per km feels at kilometre 15 rather than kilometre 2.

If your training is in miles or your watch is set to miles, convert once and keep both numbers on a band. Multiplying a per-kilometre pace by 1.609344 gives the per-mile equivalent: 4:59 per km (298.6 seconds) becomes 480.6 seconds, or 8:01 per mile.

• Do a pace rehearsal at least once, ideally 10 to 14 days before the race.
• Carry the plan on the wrist: 5 km, 10 km and 15 km checkpoints.
• Practise your race-day fuel and drink in training, not for the first time at the start line.

Setting a goal you can defend

A target that is too ambitious produces a fast start and a slow finish. A reasonable guide is to base the half marathon goal on a recent race. Predictions from a 10 km time are common, but they assume you have trained for the distance. Training with long runs and tempo runs matters more than a formula.

If you are new to the distance, pick a finish-the-race pace that feels conversational, and treat the first half marathon as a baseline. Then use the pace formula to set a goal that is a modest improvement, usually 2 to 5 percent, instead of a leap.

Anyone with a medical condition or who has not been running regularly should check with a clinician before starting a training block.