Negative Split Race Pace Calculator
Plan a negative-split race: from a target finish time and distance, get the pace for the slower first half and faster second half.
How it works
Half = distance ÷ 2 · f = 1 − split% · First-half pace = time ÷ (half × (1 + f)) · Second-half pace = first-half pace × f
A negative split means running the second half faster than the first, a pacing strategy linked to strong race results. Given a goal time and how much faster you want the back half, this solves for the two paces that still add up to your target. Set the split to 0% for an even-paced plan, where both halves share the same pace.
Worked example
For a half marathon (21.1 km) in 105 minutes with the second half 2% faster: half = 10.55 km, f = 0.98. First-half pace = 105 ÷ (10.55 × 1.98) = 5:02/km; second-half pace = 5:02 × 0.98 = 4:56/km. The halves take about 53:03 and 51:57, adding to 1:45:00.
Frequently asked questions
Why aim for a negative split?
Starting slightly conservatively spares glycogen and limits early lactate buildup, so many runners finish faster and feel stronger with a modest negative split than by going out hard.
How big should the split be?
A gentle 1–3% is realistic for most races. Larger splits require holding back a lot early, which is hard to judge and can leave time on the table if overdone.
Can I plan an even race instead?
Yes. Set the second-half speed-up to 0% and both halves will show the same pace, giving a flat even-pace plan.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.