How the splits are built
even pace = target time ÷ distance
An even split is the target time divided by the distance, and nothing more. A negative split is defined by halves: the second half is run a chosen percentage faster than the first. Inside the halves the pace here changes linearly rather than stepping at the midpoint — a race does not switch pace at a timing mat, it drifts. The linear model still hits the requested split exactly: ask for 2% on a four-hour marathon and the halves come out 2:01:13 and 1:58:47.
Why negative splits get recommended
Analyses of large marathon fields consistently show that most finishers slow in the second half, and that the slowdown concentrates after about 30 km — the 19-mile mark. Championship and record marathons, by contrast, are usually run close to even or slightly negative. The advice follows from that asymmetry rather than from any physiological law: nobody has ever regretted being able to accelerate at 35 km (22 miles), and the runners who come apart almost always did it by banking time early.
How negative is realistic
One to two percent. On a four-hour marathon a 2% negative split means starting at 5:48 per kilometre and finishing at 5:35 — 9:20 and 8:59 per mile — thirteen seconds between the first kilometre and the last full one, or about twenty-one seconds between first and last mile. That is a plan you can execute by feel. At 1% the spread is under seven seconds a kilometre. Five percent is not a pacing strategy, it is a description of a race whose first half was a warm-up. If the table asks you to run the second half dramatically faster, the target time is probably wrong rather than the plan.
The first kilometre is the one that decides
Nearly every positive split begins in the first ten minutes, when the taper has left you fresh, the field is dense, and goal pace feels absurdly easy. Running ten seconds per kilometre too fast — sixteen per mile — over the opening 5K banks less than a minute and can cost several at the end. Read the first split off the table, hold it even though it feels slow, and reassess a third of the way in.
Marathon pace chart
Even splits, with the checkpoints that most marathons actually time. Read the 30 km column — 19 miles — as the honesty check: if you reach it ahead of schedule, you did not run a smart first half.
| Target | Pace · min/km | 10 km | Half | 30 km |
|---|---|---|---|---|
| 3:00:00 | 4:16 | 42:40 | 1:30:00 | 2:07:59 |
| 3:15:00 | 4:37 | 46:13 | 1:37:30 | 2:18:39 |
| 3:30:00 | 4:59 | 49:46 | 1:45:00 | 2:29:18 |
| 3:45:00 | 5:20 | 53:19 | 1:52:30 | 2:39:58 |
| 4:00:00 | 5:41 | 56:53 | 2:00:00 | 2:50:38 |
| 4:30:00 | 6:24 | 1:03:59 | 2:15:00 | 3:11:58 |
| 5:00:00 | 7:07 | 1:11:06 | 2:30:00 | 3:33:18 |
Half marathon pace chart
Even splits for the half, with 5K checkpoints.
| Target | Pace · min/km | 5 km | 10 km | 15 km |
|---|---|---|---|---|
| 1:30:00 | 4:16 | 21:20 | 42:40 | 1:03:59 |
| 1:40:00 | 4:44 | 23:42 | 47:24 | 1:11:06 |
| 1:45:00 | 4:59 | 24:53 | 49:46 | 1:14:39 |
| 2:00:00 | 5:41 | 28:26 | 56:53 | 1:25:19 |
| 2:15:00 | 6:24 | 32:00 | 1:03:59 | 1:35:59 |
| 2:30:00 | 7:07 | 35:33 | 1:11:06 | 1:46:39 |
Both charts are generated by the same functions the calculator above uses, so nothing on this page can disagree with anything else on it.
When to abandon the table
Splits are a plan for flat ground and neutral weather. On a hilly course, run the climbs by effort and let the numbers drift — holding goal pace up a hill spends the race in the first hour. In heat the honest move is to revise the target before the start rather than to fail at it after 25 km, around 15 miles. Wind changes the cost of a pace without changing the pace itself. The table deserves to be followed exactly as long as the conditions it assumes still hold.
Frequently asked questions
What is a negative split?
Running the second half of a race faster than the first. It is expressed as a percentage: a 2% negative split on a four-hour marathon means halves of 2:01:13 and 1:58:47. It is the pacing pattern most coaches recommend and the one most recreational runners fail to execute, because it requires starting slower than you feel able to.
Should I run a marathon with even or negative splits?
Aim for even and be delighted if it turns out slightly negative. Even pacing is the simplest plan to hold and physiologically the most efficient over long distances. Deliberately planning a large negative split usually means the first half is slower than it needed to be. The practical version is to start on the conservative side of goal pace and let the second half take care of itself.
What pace is a 4-hour marathon?
5:41 per kilometre, or 9:09 per mile, held for 42.195 km. Halfway comes at 2:00:00, 10 km at 56:53 and 30 km at 2:50:38. Those numbers assume even pacing on a flat course.
How do I calculate my own splits?
Divide the target time by the distance to get the average pace, then apply it to each segment. For a negative split, decide what percentage faster the second half should be and let the pace drift linearly from slightly above average to slightly below. The calculator above does both and shows cumulative times, which is what you actually read off a watch mid-race.
Why do I always slow down after 30 km?
Three things arrive at once: glycogen runs low, the accumulated muscle damage from the impact starts to cost you, and the pace that felt controlled at 15 km (9 miles) no longer is. A conservative first half postpones all three. Fuelling from early on postpones the first. Neither can be fixed at 32 km — the 20-mile mark — which is why the plan matters more than the willpower.
Should splits be per kilometre or per mile?
Whichever the course is marked in — reading a per-kilometre plan off mile markers is how people miscalculate mid-race. The unit switch at the top of the page changes the splits table to match. Race distances themselves stay metric in both systems, because a 5K is 5 km everywhere.