Running Split Calculator

What this page does

A running split calculator answers one question: if I want to finish in x, what does each marker look like? The answer is a pace, repeated, with a running clock beside it. This page answers that question for any race distance rather than for one fixed distance, and it ends in something you can carry: the splits are drawn as a printable split band — one row per marker, and beside each row the elapsed clock you should be reading at that mark.

Two things make it general. The distance is a free number from 400 metres to 100 miles, in kilometres or miles. And the marker spacing is yours to choose — every 1 km, every 1 mile, every 5 km or every 5 miles — because a 5K and a 100-mile race do not want the same band. The table above the band and the band itself are built from the same rows, so the band is never a second calculation.

Everything runs in your browser. There is no server, no account and no upload, and the target you type never leaves the page. If your race is chip-timed and you want to know what the race clock above each marker will read while your watch reads this band, the splits calculator carries both clocks side by side.

How the number is calculated

The arithmetic is one division and one multiplication, and there is no second model behind it. For a target finish time T over a distance D, the even pace for one marker is:

p = T ÷ (D ÷ i) E_k = k × p

T — your target finish time, in seconds. 1:15:00 is 4500 s.
D — the race distance in metres. 10 miles is 16093.44 m.
i — the marker interval in metres: 1000 m for 1 km, 1609.344 m for 1 mile, 5000 m for 5 km, 8046.72 m for 5 miles.
p — the even pace per marker, in seconds.
E_k — the elapsed clock at marker k. This is the column the band prints.

Every printed time is the exact value rounded to the nearest second, except the finish row, which prints your target exactly. The page reports the largest rounding gap that actually occurs on your own band rather than quoting a generic bound.

The only numbers on this page that are not derived from your own two inputs are definitions, and they are all exact: 1 km = 1000 m; 1 mile = 1609.344 m, the international mile; a half marathon is 21.0975 km = 13.109378728227153 mi; a marathon is 42.195 km = 26.218757456454306 mi. There is no borrowed pace table, no age-grading factor and no external data file anywhere on this page.

A worked example: 10 miles in 1:15:00

The example the page opens on. Take T = 1:15:00 = 4500 s over 10 miles = 16093.44 m. The even pace is one division, and it is exact in both units:

Per mile — 4500 ÷ 10 = 450 s, printed 7:30 per mile.
Per kilometre — 4500 ÷ 16.09344 = 279.617037 s, printed 4:40 per kilometre.
Halfway — 2250 s, printed 37:30. On a 10-mile race the 5-mile marker lands exactly on it.

Change only the marker spacing and the same race produces a different band. All four are below, and each one is what the page prints for those settings:

Every 1 mile — 10 rows, 7:30 through 1:15:00, plus the finish at 10 mi. Every row is exact, so the largest rounding gap is 0.0 s.
Every 1 km — 16 rows, 4:40 through 1:14:34 at 16 km, plus the finish at 16.09344 km. The largest rounding gap is 0.4681 s, on the 4 km row (1118.4681 s prints as 1118).
Every 5 km — 3 rows: 23:18, 46:36 and 1:09:54, plus the finish. Largest rounding gap 0.2555 s.
Every 5 miles — 2 rows: 37:30 and 1:15:00, plus the finish. Largest rounding gap 0.0 s.

Note what the finish row is not. On the kilometre band it is not "17 km". The race ends at 16.09344 km, so the last segment is a partial one — 93.44 m — and the band labels it as the finish and prints your target on it exactly. Every other row carries a rounding caveat; that row does not.

A cross-check against a page you can read

The arithmetic here is deliberately the same even-split arithmetic the rest of this site uses, so a race that shares a pace with another page must print the same rows. Set the distance to a marathon and the target to 3:30:00 and the pace is 298.613580 s per kilometre — which is the identical pace a 1:45:00 half marathon runs at, because 42.195 km and 3:30:00 are both exactly twice 21.0975 km and 1:45:00. The whole-kilometre rows therefore coincide, and they coincide with the figures the half marathon split calculator publishes for its own example: 5 km 24:53, 10 km 49:46, 15 km 1:14:39, 20 km 1:39:32, 21 km 1:44:31. Two pages, one pace, same numbers — which is the cheapest available check that this page's arithmetic is not off on its own.

The band: one target, one column

What most runners call a pace band is a strip of paper with one row per marker and the elapsed clock beside it. A pace chart is the other thing: a grid with distances down one side and a range of finish times across the top. The band is the chart collapsed to the single row you actually need — your target — and turned into something wearable. This page draws that strip for whatever distance and marker spacing you asked for.

Three design choices are worth naming, because they are where bands differ from each other.

Elapsed, not lap. The table above has both columns; the band carries only elapsed. On race day you are comparing one number — the total on your watch — against one number on the band, while breathing hard. A lap column asks you to subtract mid-race, and it also lets ten separate small errors sit side by side looking harmless, whereas a cumulative column makes drift accumulate where you can see it.
One second, not five. Every row is the exact time rounded to the nearest second, so no row can be more than half a second from the arithmetic, and the page reports the largest gap on your band. Many printed bands round to the nearest five seconds to be easier to read at a glance, which widens the worst case on a single row to 2.5 s. This page keeps the half-second bound instead; if you would rather have the five-second version, the arithmetic is all on this page.
Your marker spacing. The band follows the interval you chose rather than forcing a row per kilometre. A marathon is a 43-row strip at 1 km, 27 rows at 1 mile, 9 rows at 5 km and 6 rows at 5 miles — the same race, four bands, and only you know which one you would actually wear.

There is a hard cap on the length. The page draws at most 60 rows and refuses anything longer with a message, rather than quietly cutting rows off the end of the band. If your distance needs more, widen the interval: a 100-mile race is 161 rows at 1 km, 101 rows at 1 mile, 33 rows at 5 km and 21 rows at 5 miles. That is a deliberate limit on an honest failure, not a hidden one.

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 ground between two markers. It has a firm opinion about the clock at the marker, 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 46:36 at 10 km and your watch says 46:36, you are on the band. If your watch says 46:42, 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.

Two practical notes on carrying it. The band is drawn 170 mm wide and carries a 50 mm scale check near the top: print it, hold a ruler against that line, and if it measures 50 mm the band is the size it was drawn — print dialogs default to "fit to page", which resizes it. And on a long race the strip is long: at 1 km markers a marathon band is a folded sheet rather than a wristband, which is exactly why the 5 km and 5-mile intervals exist. Fold down the middle and the start and finish end up at opposite ends of the strip.

If you have no printer to hand, Download band writes the same rows to a plain-text file and Copy splits puts them on your clipboard. Neither is a substitute for the printed strip — a phone in a pocket at 30 km is not a band — but the text file is the version to keep, and it reprints identically whenever you want it.

Supported range and limits

Distance: 0.4 km to 160.9344 km (400 metres to 100 miles), in kilometres or miles. The unit control sets how you enter it; the arithmetic converts to metres either way.
Target time: 1 minute to 47:59:59, entered as hours, minutes and seconds, with minutes and seconds between 0 and 59.
Marker intervals: 1 km, 1 mile, 5 km or 5 miles. Those four only — there is no custom interval field.
Band length: up to 60 rows, counting the finish row. Longer than that and the page says so instead of drawing a band.
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 hill adjustment. The band assumes a flat course and says so on every row. A hilly course needs a per-kilometre elevation profile and a published energy-cost model; the marathon split calculator does that for the marathon, and the race time calculator does it for a course you are aiming at. This page does not borrow their model, because a band that quietly mixes two models is worse than a band that states one.
No second clock. The band carries one clock, the one you keep. If your race is chip-timed and you want to know what the gun clock above each marker reads, the splits calculator carries both.
No negative splits. A band carries one target and one number per row; a negative split is a shape, not a target, and printing one needs a model of how much slower the first half should be. That would be a guess about you, so the page prints the honest version — even splits — and leaves the shape to you. The predictor on the home page does offer a negative-split toggle for its own table, and it says what assumption that toggle makes.
No prediction. This page starts from a target time you already believe. It does not tell you what you are capable of: the race time predictor moves a recent race result along the distance curve, and the race time calculator prices the course on top of it.
No aid-station markers. Real bands sometimes mark where the water is. That needs one race's aid-station positions, 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 "Berlin" option. A preset would mean shipping a per-kilometre profile for a real course, and courses are re-measured.
No age grading and 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 running split calculator?

A running split calculator turns one number — the finish time you are aiming for — into the clock you should be reading at each marker of the course. This one is distance-free: enter any race from 400 metres to 100 miles, choose whether the markers are kilometres or miles, and it prints the splits and then draws them as a band you can print and wear.

How do I use the band on race day?

Read the elapsed column, not the lap column. At each marker, compare the total time on your watch with the band's number for that marker. Because the band is cumulative, a small per-marker error shows up at the next row instead of hiding inside one lap. The band tells you where you are; deciding whether to change anything is yours.

Why are the splits the same for every marker?

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. A band carries one target and one number per row, and a pacing model that varies the pace would need assumptions about your course and your fitness that this page does not have and will not invent.

Can I have the band every 5 km or every 5 miles?

Yes. The marker control offers 1 km, 1 mile, 5 km and 5 miles, and the band and the table both rebuild around whichever you pick. A 100-mile race at 5-mile markers is a 20-row band; the same race at 1-mile markers is 100 rows, which is more than a band can hold, and the page says so rather than truncating it.

Why is there a limit on the number of rows?

A band is a strip you fold and carry, so the page draws at most 60 rows and refuses anything longer instead of quietly cutting rows off the end. If your distance needs more, choose a wider marker interval: 100 miles is 161 rows at 1 km, 101 at 1 mile, 33 at 5 km and 21 at 5 miles.

Does this work for a hilly course?

No. The band assumes a flat course and says so. A hilly course needs a per-kilometre elevation profile and an energy-cost model, and the marathon split calculator and the race time calculator on this site do that job. This page does not borrow their model, because a band that quietly mixes two models is worse than a band that states one.

Does it tell me what I can run?

No. This page starts from a target time you already believe and turns it into splits. Predicting what you are capable of is a different job: the predictor on the home page moves a recent race result along the distance curve, and the race time calculator prices the course you are aiming at.

Every split

Your printable split band