Marathon Pace Calculator (26.2 Miles)

The marathon is 26 miles 385 yards — 26.22 miles, or 42.195 km — a distance World Athletics froze in 1921 after the 1908 London course was stretched to suit a royal viewing box. Enter your goal time to get the pace that covers it.

Worked example: four hours

Pace = time ÷ distance = 240:00 ÷ 42.195 km = 5:41/km, or 10.55 km/h and 9:09 per mile.

Hold it exactly and you cross at 3:59:48, because 5:41 rounds down from the true requirement. That 12-second cushion is the entire margin the round number gives you.

Goal times and their paces

Goal time	Pace (min/km)	Pace (min/mile)	Speed
3:00	4:16	6:52	14.06 km/h
3:30	4:59	8:01	12.06 km/h
4:00	5:41	9:09	10.55 km/h
4:30	6:24	10:18	9.38 km/h
5:00	7:07	11:27	8.44 km/h
5:30	7:49	12:35	7.67 km/h

The fade is the default, and it has a size

Researchers took 14 US marathons from a single year and analyzed 91,929 finishes, measuring each runner’s second-half pace against the first. The average change was 15.6% slower for men and 11.7% for women — a gap that held in all 14 races, across age groups and finishing times, and survived every adjustment the authors made. They defined holding the pace as slowing by less than 10%, and marked slowing as 30% or more.

Put that number into a four-hour plan and the cost becomes concrete. Start at 5:20/km, a mere 21 seconds per kilometer quicker than goal pace, then fade by the male average:

Segment	Pace	Split
First half	5:20/km	1:52:31
Second half	6:10/km (15.6% slower)	2:10:04
Total	—	4:02:36

Twenty-one seconds of early greed bought a 2:36 miss. The women’s average fade, applied to the same opening, still lands at 3:58:12 — which is the practical case for pacing conservatively rather than an argument about physiology.

What the fade is made of

Slowing in a 10K is mostly a decision. In a marathon it is also chemistry: glycogen runs out, muscle damage accumulates, and heat load builds for hours. Those are the reasons the second half punishes a fast start so much harder here than at any shorter distance, and why fueling and starting pace are the two variables worth obsessing over.

Build the plan in two halves

The negative split calculator lays out the alternative — a first half deliberately slower than goal pace, with the reserve spent after the 30 km mark. Rehearse it at the half marathon pace calculator distance first, where a pacing error costs minutes instead of an afternoon. For any other distance, the running pace calculator does the same math.