Marathon Time Calculator

Marathon finish time: T = pace × 42.195 km

Since a marathon covers 42.195 km, your predicted finish is just T = pace × 42.195. The usual benchmarks: sub-3 needs a pace of 4:15/km or faster, sub-4 wants 5:41/km, and sub-5 sits at 7:06/km. When you only have a shorter race to go on, Riegel's formula T₂ = T₁ · (D₂/D₁)^1.06 lets you project from a 10K or half-marathon (HM). That 1.06 exponent is what accounts for the extra fatigue you pick up over longer distances. So a 45-min 10K works out to roughly 3:28 over the full marathon. The world record belongs to Eliud Kipchoge, who ran 2:00:35 in Berlin 2022 (later bettered by Kelvin Kiptum at Chicago 2023). And here's the thing about pacing: staying consistent beats raw top-end speed, because big positive splits will usually cost you more than 5 minutes.

Applications

Use it to plan race day for the International Marathon of São Paulo, Maratona do Rio, Boston, Berlin or New York. It also helps set training paces for your long runs, check the race predictions Strava and Garmin throw at you, plan a BQ (Boston qualifier) attempt, or print a pace band with your kilometer splits.

FAQ

Why does Riegel use 1.06 and not 2? The number came out of fitting real runner data. An exponent of 2 would mean your time doubles every time the distance doubles, which is far too pessimistic. The 1.06 value tracks the actual aerobic fatigue curve trained athletes experience.

Can I just double my half-marathon time? Don't. Doubling tends to undershoot your real marathon time by 5 to 15 minutes. The culprit is the "wall" that hits around km 30–35, when your glycogen runs low.

What if I run negative splits? Running the second half faster than the first usually drops your total time, and it tends to feel easier on the body too. That's why most of the elite world records came from even or slightly negative splits.