Half Marathon Split Calculator

What this page does

A half marathon split calculator normally answers one question: if I want to finish in x, what does each kilometre look like? The answer is a pace, repeated twenty-one times, with a running clock beside it. That answer is correct, and it is also the least useful thing you can carry on race day, because you cannot read a browser tab at 18 km.

This page keeps the clock and hands it to you on paper. Type your target finish time and it builds the splits for the 21.0975 km half marathon, then draws them as a printable pace band — one row per kilometre or mile, and beside each row the elapsed clock you should be reading at that mark. Cut it out, fold it, tape it on. The band is the deliverable; the table above it is how you check the band.

Everything runs in your browser. There is no server, no account and no upload, and the target time you type never leaves the page.

How the number is calculated

The arithmetic is one division, repeated. The half marathon is 21.0975 km, so the even pace for a target time T is:

p = T ÷ D where D = 21.0975 km (or 13.1094 mi)

T — your target finish time, in seconds. 1:45:00 is 6300 s.
D — the half marathon distance: 21.0975 km exactly, which is 13.1094 mi. The 21.0975 km figure is the official road-race distance, not a measurement of any one course. The mile figure is that distance converted at 1 mi = 1609.344 m, which is the exact international mile.
p — pace per kilometre or per mile, in seconds.

From there, every row of the band and every row of the table is the same two lines of arithmetic:

E_k = d_k × p L_k = (d_k − d_k−1) × p

d_k — the distance at marker k, in kilometres or miles. For the kilometre band these are 1, 2, 3 … 21, and then the finish at 21.0975.
E_k — elapsed: the clock reading at marker k. This is the column the band prints.
L_k — lap: the time for that segment alone. This is the column the table prints.

A worked band: 1:45:00

Take T = 1:45:00 = 6300 s. The even pace is 6300 ÷ 21.0975 = 298.61 s per kilometre, which is 4:58.6 — printed on the band as 4:59. The same target over 13.1094 miles is 480.57 s per mile, or 8:00.6. The elapsed column then falls out of the multiplication:

5 km — 5 × 298.61 = 1493.1 s, printed 24:53.
10 km — 2986.1 s, printed 49:46.
15 km — 4479.2 s, printed 1:14:39.
20 km — 5972.3 s, printed 1:39:32.
21 km — 6270.9 s, printed 1:44:31.
Finish, 21.0975 km — 1:45:00, printed exactly, with no rounding, because the finish row is your target.

The halfway point of a half marathon is 10.54875 km, and on even splits it is exactly half the target — 52:30. If you are reading 52:30 as you cross the halfway line, you are running the band precisely.

The pace band: one target, one column

A half marathon pace chart is a grid: distances down one side, a range of finish times across the top, and a pace in every cell. It is a reference document. A pace band is the opposite — it collapses that grid to the single row you actually need, which is the row for your target, and turns it into something you can wear. The whole design difference is in that collapse, so it is worth being exact about what the band contains.

The band has one row per whole kilometre, plus one row for the finish:

Kilometre band — 21 whole-kilometre rows (1 km through 21 km) plus the finish at 21.0975 km. 22 rows.
Mile band — 13 whole-mile rows (1 mi through 13 mi) plus the finish at 13.1094 mi. 14 rows.

Note what the last row is not. It is not "22 km" or "14 mi". The race ends at 21.0975 km, so the final segment is a partial one — 97.5 m on the kilometre band — and the band labels it as the finish and prints your target time on it exactly. Every other row is rounded to the nearest second, so the last row is the one row you can trust to the second without a rounding caveat.

The band prints elapsed, not lap — and that is the point

The table above the band has both columns. The band carries only elapsed. That is deliberate: on race day you are comparing one number — the total time on your watch — against one number on the band, and you are doing it while breathing hard. A lap column asks you to subtract the previous row from the current one, mid-race, which is exactly the kind of arithmetic that goes wrong at 16 km.

There is a second reason. A cumulative column cannot hide a small error. If you run each kilometre three seconds slow, the band's 10 km row is thirty seconds away from where you are, and it is visibly away. A lap-only band would let ten separate three-second errors sit side by side looking harmless. The band is built so that drift accumulates where you can see it.

The rounding rule, and the bound it gives you

Every printed time is the exact even-split time rounded to the nearest second. Rounding to the nearest second means the error on any single row cannot exceed half a second in either direction, and the page reports the largest gap that actually occurs on your band — for the 1:45:00 example above it is 0.5 s, at the 9 km row, where the exact 2687.5 s prints as 2688.

That is a stated guarantee rather than a hope, and it is a design choice worth naming: many printed bands round each row to the nearest five seconds, which makes the numbers easier to read at a glance but widens the worst-case error on a single row to 2.5 s. This page rounds to one second and keeps the half-second bound instead. If you would rather have the five-second band, round each row yourself — the arithmetic is all on this page.

Reading the band on the day

The band is a measuring stick, not a coach. Three things follow from that, and they are the whole of how to use it:

Read the elapsed column at the marker, not between markers. The band has no opinion about the 400 m between kilometre 7 and kilometre 8. It has a firm opinion about the clock at kilometre 8, and that is the number to compare with your watch.
A gap smaller than the rounding bound is not a gap. If the band says 49:46 at 10 km and your watch says 49:46, you are on the band. If it says 49:46 and you are at 49:52, you are six seconds down — real, but small, and the band's job ends at showing you that.
The band does not tell you to catch up. It tells you where you are. Whether to press, hold or ease is a decision about your fitness and the course, and nothing in a table of even splits knows either of those things.

The halfway check is the one row worth marking on the band in pen before you start. Half of 21.0975 km is 10.54875 km, and on even splits the halfway clock is exactly half your target — 52:30 for a 1:45:00 goal. It sits between the 10 km row (49:46) and the 11 km row, 548.75 m past the 10 km mark. Most races have a halfway timing mat; if yours does, that mat and the band should agree to within the rounding bound.

One honest caveat sits on top of all of it. Even splits assume the second half is run at the same effort as the first, and the single most common way a half marathon goes wrong is a first half run too fast. A band cannot stop that — but it can show it to you at 10 km, which is earlier than most runners notice.

Printing the band at the right size

A pace band that prints at the wrong scale is not a pace band; it is a smaller or larger piece of paper with the same numbers on it. The band is drawn 170 mm wide, and it carries its own scale check: a line marked "this line is 50 mm" near the top. Print the page, then hold a ruler against that line. If it measures 50 mm, the band is the size it was drawn. If it does not, your printer scaled the page and the band is the wrong size.

Set the scale to 100%. Print dialogs default to "fit to page" or "shrink to fit", and both will resize the band. Choose 100%, Actual size, or "none" depending on the dialog. This is the one setting that matters.
A4 and US Letter both work at 100%. The band is 170 mm wide and about 95 mm tall, so it fits inside the printable area of either sheet with room to spare.
Fold down the middle. The rows run in two columns: the left column is the first half of the race, the right column is the second half and the finish. Fold between them and the start and the finish end up at opposite ends of the strip.
Cut along the border, then tape the ends. The strip is 170 mm long — about the circumference of an adult wrist — so the two ends meet with a small overlap to tape. If you would rather not wear it, it is the right size to sit flat in a pocket or a race-belt sleeve.
Black and white is fine. Nothing on the band depends on colour; the highlighted rows are shaded, and they survive a monochrome printer.

If you have no printer to hand, the Download band button writes the same rows to a plain-text file, and Copy pace band puts them on your clipboard. Neither of those is a substitute for the printed strip — a phone in a pocket at 15 km is not a pace band — but the text file is the version to keep, and it reprints identically whenever you want it.

Supported range and limits

Distance: the half marathon only — 21.0975 km or 13.1094 mi. This is not a general distance calculator; the whole point is that the distance is fixed and the band is built for it.
Target time: 5 minutes to 47:59:59, in hours, minutes and seconds. Below five minutes the page refuses the entry rather than printing a band for a time no half marathon has been run in.
Units: kilometres or miles for the band and the table, switchable at any time. The distance behind the two is the same; only the markers move.
Pacing: even splits only. There is no negative-split band, and the reason is in the next section.
Cost: none. No account, no email, no paywall, no daily limit, no request to a server.
Privacy: every number is computed in your browser. Nothing you type is sent anywhere or stored — reload the page and it is gone.
Works offline once the page has loaded, and on a phone.

What this page deliberately does not do

No negative-split band. A band carries one target time and one number per row; a negative split is a shape, not a target, and printing it needs a model of how much slower the first half should be. That model would be a guess about you, so the page prints the honest version — even splits — and leaves the shape to you.
No hill adjustment. The band assumes a flat course and says so on every row. A hilly half needs a per-kilometre elevation profile and an energy-cost model; the marathon split calculator does that job for the marathon, and this page does not borrow it, because a band that quietly mixes two models is worse than a band that states one.
No aid-station markers. Real bands sometimes mark where the water is. That requires the aid-station positions for one specific race, and this page has no source it can stand behind for any race's layout, so it prints distance markers only.
No course presets. There is no "Boston" or "Great North Run" option. A preset would mean shipping a per-kilometre profile for a real course, and courses are re-measured.
No watch or GPS sync. Nothing here connects to a device. The band is a piece of paper and the comparison is by eye.
No age grading, no weather correction. Both need published tables or models this page does not have. Rather than ship a made-up coefficient, it leaves them out and prints the number it can defend.

Questions

What is a half marathon split calculator?

It turns one number — the finish time you are aiming for — into the pace and elapsed clock for every kilometre or mile of the 21.0975 km half marathon. This page does that and then goes one step further: it draws the result as a printable pace band, so the splits end up on your wrist instead of in a browser tab.

What is a half marathon pace band?

A pace band is a strip of paper carrying one row per marker — every kilometre or mile — and beside it the elapsed clock you should be reading at that mark. It is a half marathon pace chart reduced to a single target time and a single column, sized to be cut out and worn. This page prints the band itself, with a 50 mm scale check on it so you can tell whether your printer kept the page at 100%.

How do I use the band on race day?

Read the elapsed column, not the lap column. At each kilometre or mile marker, look at the total time on your watch and compare it with the band's number for that marker. Because the band is cumulative, a small per-kilometre error shows up at the very next row rather than hiding inside a single lap. The band tells you where you are; deciding whether to change anything is yours.

Why are the splits the same for every kilometre?

Because the band is built on even splits — one pace, repeated, on the assumption that the course is flat and you can hold a constant effort. That is a deliberate choice, not an oversight. A band has one target time and one number per row; a pacing model that varies the pace needs assumptions about your course and your fitness that this page does not have and will not invent.

Is a half marathon 13.1 miles?

The half marathon is defined as 21.0975 km, which is 13.1094 miles — the 13.1 that races and watches use. Switch the unit control to Miles and the band is marked in whole miles with the finish row at 13.1094 mi. The underlying distance does not change; only the markers do.

Can I get the band in miles instead of kilometres?

Yes. Choose Miles and the band carries 13 whole-mile rows plus the finish at 13.1094 mi, and the splits table switches to mile laps and mile pace. Everything is rebuilt in the browser, so switching back and forth costs nothing.

What about a hilly half marathon?

This band assumes a flat course and says so. If your half has real climbing, the even splits it prints will be too fast on the climbs and too slow on the descents. A separate page on this site handles hill-adjusted splits for the marathon using a published energy-cost model; the band here deliberately stays on even splits rather than borrowing a model it cannot verify per kilometre for your course.

How accurate are the times on the band?

Each printed time is the exact even-split time rounded to the nearest second, so no row can be more than half a second away from the arithmetic — the page reports the largest gap on your own band. The finish row is printed with your target time exactly. The band's accuracy as a race plan is a different question: it assumes you run the first half no faster than the second, which is the assumption most runners break.

Every split

Your printable pace band