Negative Split Calculator
Plan a negative split for any race. Enter your goal time and how much faster you want the second half — get first/second-half paces and a full split table. Free.
The % is how much faster your second half runs versus your average pace. 1–3% is typical.
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What a negative split is
A negative split means running the second half of a race faster than the first. Enter your race distance, goal finish time, and the percentage by which you want the back half to be quicker, and this calculator gives you the exact first-half and second-half times, the pace for each, and a full mile-by-mile (or km-by-km) split plan.
A 2% negative split is a sensible, achievable target for most runners. On a 2:00:00 half marathon that means running the first half in about 1:01:12 and the second in about 58:48 — roughly 11 seconds per mile slower than goal pace early, then 11 seconds per mile faster late. Small on paper, decisive in practice.
Why negative splits work
The fastest marathons and half marathons in history are almost all run as even or slightly negative splits. The reason is physiological: starting a touch slower keeps your early effort below the threshold where you accumulate fatigue-causing byproducts and burn through glycogen too fast. You bank no time by going out hard — you only borrow it, at ruinous interest, from the final miles.
The most common way to wreck a race is the opposite, a positive split: going out too fast, feeling great for 30 minutes, then watching the pace bleed away as the legs give out. Nearly every recreational runner does this at least once. A negative split is the discipline that prevents it. The hard part isn’t the math — it’s holding back when you feel fresh and everyone around you is surging.
How to actually run one
- Know your goal pace before the start. Use the Pace Calculator or check your fitness with the VDOT Calculator so your goal is realistic, not aspirational.
- Start in the slower half-pace this calculator gives you, and hold it even if it feels too easy for the first few miles. It’s supposed to.
- Settle into goal pace through the middle.
- Pick it up over the final third, spending whatever you have left.
For a deeper tactical breakdown — including how to handle hills and aid stations — read the Half Marathon Negative Split Strategy guide, then build your race-day plan with the Race Split Planner.
Want all of this in your pocket, offline, with no subscription? Pacesmith is a $1.99 iOS app — VDOT zones, race predictions, pace math, and split planning, no internet required, one-time purchase.