Running / 004
Marathon pace calculator
A goal time in, the pace you have to hold out — or a pace in and the finish time it gives you. Distance fixed at 42.195 km, with every checkpoint from 5K to the line.
Read the guide: a marathon pace chart from 2:30 to 6:00, with half, 10K and 30K splits
Required pace
Even paceCheckpoint splits
Halfway| Split | Cumulative time |
|---|
Next / Race day
Build the rest
of the plan.
Running pace
Any distance, not just the marathon, plus training paces off the result.
Heart rate zones
Check the effort behind the pace, in beats per minute.
Race time predictor
Not sure of the goal yet? Work one out from a race you have already run.
VO2max
What the aerobic engine can do, from a short test rather than a long one.
One-rep max
For the strength work that holds the running together.
The arithmetic, written out
Pace is the finish time divided by the distance: pace = time ÷ 42.195 km. A three-hour marathon is 10,800 seconds over 42.195 km, which is 255.95 seconds per kilometer, displayed as 4:16/km. In miles the distance is 42.195 ÷ 1.609344 = 26.2188, so the same three hours is 411.92 seconds per mile, displayed as 6:52/mi. The mile figure is derived from the kilometer figure rather than typed in, so the two can never disagree.
Going the other way, finish time is pace multiplied by distance. Five minutes per kilometer over 42.195 km is 12,658.5 seconds, which is three hours, thirty minutes and 58.5 seconds.
Rounding. Every figure is calculated at full precision and rounded only for display, to the nearest whole second, with a half second going up. That is why 12,658.5 seconds shows as 3:30:59 and not 3:30:58. Checkpoint times are each computed from the unrounded pace rather than by adding rounded splits together, so the error cannot accumulate down the table and the finish line always matches the time you asked for.
Even pace, and the alternative
Unless the negative split toggle is on, every split on this page assumes you hold one pace from the gun to the line. That is the plan that is easiest to execute and hardest to wreck, and it is the one the splits are built for.
The negative split option asks how many seconds per kilometer slower you want the first half, then takes the same amount off the second half. Because the two adjustments are equal and opposite over equal distances, the halves still add up to exactly the goal time: five seconds per kilometer down for 21.0975 km and five up for the other 21.0975 km finishes at the same instant as holding even throughout. What changes is the shape of the effort, not the total.
These are arithmetic targets, not a race strategy and not coaching. A pace that divides neatly on a page still has to be held on a particular day, on a particular course, in whatever weather turns up, by a body with its own opinion. Hills, heat, wind and how the training actually went all matter more than the third decimal place. Talk to a doctor before you train for or race one of these if your heart or lungs give you trouble, if you are coming back from injury, or if you have never covered the distance.
Common questions
What pace do I need for a sub-3 marathon?
Three hours over 42.195 km is 4:16 per kilometer, or 6:52 per mile. That is 10,800 seconds divided by the distance, and it has to hold for the whole way — the figure assumes you cross the line at the same speed you passed 5K. Most people who miss a round-number goal do not miss it by being too slow early.
Should I run a marathon at even pace?
This page assumes an even pace, because that is the easiest plan to execute and the hardest to wreck. The common failure is the opposite: banking time in the first half, then giving back more than was banked over the last ten kilometers. If you want to plan a deliberate negative split, the toggle on this page builds one that still adds up to your goal time.
How does the negative split option work?
You choose how many seconds per kilometer slower to run the first half. The second half is made faster by the same amount, so the two halves still sum to exactly your goal time — running the first half five seconds per kilometer down and the second half five up finishes at the same moment as holding even pace throughout. The splits table and both half paces update to match.
Why does my watch disagree with these splits?
Almost always because of distance, not pace. A GPS watch measures the line you actually ran, and weaving through a field, running wide on bends and missing the tangents all add up — finishing a certified course with 42.5 or 42.7 on the watch is ordinary. Your average pace then looks faster than the pace these splits called for, while your finish time is unchanged.
How are the splits rounded?
Pace is worked out at full precision and only the displayed figures are rounded, each to the nearest whole second, with a half second going up. Checkpoint times are computed from the unrounded pace rather than by adding up rounded splits, so the rounding does not accumulate down the table and the finish line always matches the goal time you entered.