Negative Split Calculator

How it is calculated

The tool starts from your average pace for the goal time: avg = total seconds / distance (km). The split percentage is the total pace difference between the two halves, shared evenly around the average: first pace = avg × (1 + split / 200) and second pace = avg × (1 − split / 200). Each half covers half the distance, so half time = half pace × distance / 2. The gap shown is first-half time minus second-half time, which equals total × split / 200. Distance is in km, the goal time in hours, minutes and seconds (they add up). If the split is left empty, 2 % is used; 0 gives an even split, and values from 0 up to just under 50 are accepted. A goal that needs a pace faster than 1:30 per km, a zero time or a zero distance gives no result. Times are rounded to the second.

Common mistakes

• Reading the split percentage as how much faster the second half is than the first. It is the total gap between the halves relative to average pace, so each half sits half of it away from the average.
• Putting the goal time for a different distance, such as a half-marathon time with the marathon distance. Every pace follows from time divided by distance, and an impossibly fast pace gives no result.
• Entering the distance in miles. The field is km, and 26.2 miles would be treated as 26.2 km.
• Filling hours, minutes and seconds with overlapping totals. They add up, so 3 hours plus 210 minutes is 6:30:00, not 3:30:00.
• Running the first half at exactly the planned pace on a hilly course. The plan is flat-ground arithmetic, with no hill, wind or heat adjustment.