Marathon Pacing: Even, Negative, and Positive Splits With a 3:45 Goal
October 29, 2026
The marathon distance is 26.2188 miles (42.195 km). A goal time of 3:45:00 is 13,500 seconds, so the even pace is 13,500 ÷ 26.2188 = 514.9 seconds per mile, or 8:34.9 per mile (5:20 per km). The halfway point (13.1094 miles) comes at 1:52:30 for an even-paced race.
Most runners slow down in the second half. Coaches usually recommend an even or slightly negative split (second half faster).
Skip the math and get your answer instantly:
Open the Pace Calculator →Three Strategies for the Same Finish Time
Even split: 8:35 per mile all the way, halves of 1:52:30 and 1:52:30. Negative split: run the first half 6 seconds per mile slower than average, and the second half 6 seconds faster: 8:37.9 per mile for the first half (1:53:09) and 8:31.9 per mile for the second (1:51:51), a total of 3:45:00. Positive split: start fast at 8:14 per mile and hit halfway in 1:48:00, which feels great but leaves 1:57:00 for the second half to still finish in 3:45 (8:56 per mile), a slowdown of about 41 seconds per mile. In practice, runners who start that fast often fade much more than that, finishing in 3:55 or slower.
| Strategy | First half | Second half | Pace first half | Pace second half |
|---|---|---|---|---|
| Even | 1:52:30 | 1:52:30 | 8:35 | 8:35 |
| Negative (6 s/mi) | 1:53:09 | 1:51:51 | 8:38 | 8:32 |
| Positive (fast start) | 1:48:00 | 1:57:00 | 8:14 | 8:56 |
Why Starting Fast Costs More
Glycogen depletion and muscle fatigue are non-linear: going 30 seconds per mile too fast in the first half can cost 60 to 90 seconds per mile later, because the body runs low on stored fuel around mile 18 to 22. A 10-mile section run 20 seconds per mile faster than planned saves 200 seconds but typically costs several times that later. Starting conservatively, by about 5 to 10 seconds per mile slower than goal pace for the first 3 miles, usually preserves the ability to speed up or hold the pace. Heat, hills, and wind also change the pace: adjust the effort and not the clock.
Setting Up a Pace Plan
Write a pace band with the mile or kilometer splits. Check your watch against course markers, as GPS often records slightly more than 26.2 miles because of tangents. Practice goal pace on long runs, and take in carbohydrates (30 to 60 g per hour) at planned intervals. If you feel strong after mile 20, then you can speed up. Account for aid stations and bathroom stops in the plan.
Realistic Goals
A common predictor: marathon time ≈ 2.1 × half-marathon time, or based on a recent 10K with the Riegel formula T2 = T1 × (D2/D1)^1.06. A 50-minute 10K predicts 50 × 4.2195^1.06 = 50 × 4.60 = about 3:50 for the marathon. Training volume and experience are decisive.
Frequently Asked Questions
What pace is needed for a 3:45 marathon?
About 8:35 per mile (5:20 per km).
What is a negative split?
Running the second half faster than the first.
Why is a fast start risky?
It depletes glycogen and often causes a larger slowdown later.
How can I predict my marathon time?
From a recent race using the Riegel formula, with caution.
Why do GPS watches show more than 26.2 miles?
Because of the path taken around corners and the GPS error.