Negative Split Planner
Enter your goal distance and finish time, then set how much faster you want the second half to be. Get a first half and second half time and pace to race by.
Split difference as
First half
Pace: 5:05 /km
Second half
Pace: 4:53 /km
Difference: 4:12 faster second half, a 2% negative split.
This estimate uses a generic formula. Connect your Strava/Whoop/Garmin data for a version personalised to your actual training.
Get early accessWhy runners plan negative splits
A negative split means running the second half of a race faster than the first. Holding back early keeps you from burning glycogen and accumulating fatigue before the race is half over, which leaves more in reserve for the back half, when most runners who went out too hard are already fading. It is a deliberate strategy, not a guess: this planner turns a target split difference straight into the first half and second half time and pace you should actually race.
How big a difference is realistic
A small, disciplined negative split, roughly 1 to 3% of goal time, is realistic for most trained runners and is the range elite marathoners often run. Pushing much past that asks for a lot of held back effort early, which is harder to execute than it sounds standing at the start line: you will feel comfortable, maybe too comfortable, for the whole first half. If you are newer to pacing a race, start with a smaller difference, or an even split, and save a true negative split for once you have a few race results to calibrate against.
How it is calculated
Even pace = Goal time ÷ Total distance. First half pace = Even pace × (1 + p), second half pace = Even pace × (1 − p), where p is your split difference expressed as a fraction of goal time. Entering the difference in seconds instead of percent just solves for p first: p = (seconds difference) ÷ (goal time in seconds). Because both halves cover equal distance, the two adjustments always cancel out, so the total still lands exactly on your goal time no matter how big a difference you set.
Sources and limitations: see our methodology. Once you have a plan, build it into a full checkpoint-by-checkpoint split table and pace band.
Worked example
Take a runner aiming for a marathon in 3:30:00, planning a 2% negative split:
The two halves still add up to exactly 3:30:00. From here, the plan is simple to race by: run the first 21.1 km at 5:05 /km, then pick it up to 4:53 /km for the second half.
FAQ
How much should I negative split a marathon?
A common, achievable target is a 1 to 3% negative split, meaning your second half is 1 to 3% of your total goal time faster than your first half. For a 3:30:00 marathon, that is roughly 2 to 6 minutes faster over the back half. Bigger negative splits are possible but demand real discipline holding back early.
Is a negative split actually faster than running even pace?
For the same average pace, a negative split and an even split finish in the same total time, since both are just different ways of distributing the same goal time across the distance. The advantage of a negative split is physiological, not arithmetic: holding back early tends to produce less fatigue and fewer blowups late in a race than starting at or above goal pace.
Should I plan my split difference in seconds or percent?
Percent scales naturally with your goal time, so the same percentage means a bigger buffer in a marathon than a 5K. Seconds is more concrete if you are thinking in checkpoint terms, like wanting to run the second half exactly 90 seconds faster. Both modes here compute the same underlying plan, so use whichever is easier to reason about for your race.
What is a 3-stage progressive pacing plan?
Instead of two halves, a progressive plan splits the race into thirds: a slightly slower first third, an even-pace middle third, and a slightly faster last third. The outer two thirds cancel out the same way the two halves do in a standard negative split, so the total still lands exactly on your goal time, just with a gentler, more gradual pickup instead of one switch at halfway.
How do I turn this plan into checkpoint splits I can race with?
Once your first half and second half times are calculated, use the "Build the full km/mi table and pace band" button to carry the same distance, goal time, and split difference straight into the Split Calculator, which breaks the plan into a checkpoint-by-checkpoint table and a printable pace band.