How it works
Even pacing is simple: divide the goal time by the distance and run every split at that pace. A 4:00:00 marathon is 5:41 per kilometer from start to finish.
A negative split means running the second half faster than the first. Rather than switching pace at halfway, this calculator changes pace a little at a time, so each split is slightly quicker than the one before and the total still adds up to your goal. A positive split does the reverse.
The Elapsed column is the one to use on race day. It tells you what your watch should read as you pass each marker, which is easier to check mid-race than individual split times.
The formula
average pace p = goal time ÷ distance D
pace at point x p(x) = p × (1 + s × (1 − 2x ÷ D))
negative split by d: s = 2d ÷ (2 − d)
positive split by d: s = −2d ÷ (2 + d)
even pace: s = 0
split time = pace added up over that stretch of the courseWith this shape, the second half is exactly d faster or slower than the first half, and the total always equals the goal time.
Worked example
Goal: a 4:00:00 marathon with a 2% negative split.
- Average pace is 4:00:00 ÷ 42.195 km = 5:41 per km.
- For d = 2%, s = 0.04 ÷ 1.98 = 0.0202. You start at about 5:48 per km and finish at about 5:34 per km.
- The first half takes 2:01:13 and the second half 1:58:47, which is 2:25 quicker, or 2% of the first half.
- The final split is the last 195 meters, which takes about 1:05.
Questions
What is a negative split?
Running the second half of a race faster than the first. A positive split is the opposite, where you slow down in the second half. Even splits keep the same pace throughout.
Should I plan even or negative splits?
Starting faster than goal pace tends to cost more time late in the race than it saved early on, which is why many runners plan an even pace or a small negative split. On hilly or windy courses, aim for even effort rather than even pace.
How big should the difference be?
Small numbers go a long way. A 2% difference on a 4-hour marathon is about two and a half minutes between the halves. Settings above 5% are rarely useful for road races.
Why is the last split shorter?
Race distances rarely divide evenly into kilometers or miles. A marathon ends 195 meters after the 42 km marker, and 0.2 miles after the 26 mile marker. The table marks that final part split.
How do I take the splits with me?
Copy the link to save your plan, or write the elapsed times for a few key markers, such as every 5 km, on a pace band or your hand.