How to use race splits
Even splits divide your target time equally across every mile (or kilometer). For a 3:30 marathon that is 8:01 min/mile (4:59 min/km), so you should pass 10 miles at 1:20:06, halfway at 1:45:00 and 20 miles at 2:40:11. The split calculator lists every marker so you can write the numbers on a pace band or memorize the checkpoints your race provides.
Why even pacing works. Nearly every distance world record was set with even or slightly negative splits (second half marginally faster). Starting faster than target pace feels free for the first miles and is paid back with interest after mile 20. The plan here is the baseline; experienced runners subtract 3–5 seconds per mile in the first half on a fast course and add it back in the second.
Miles or kilometers. Use the unit toggle to switch. Races in the US, UK and Australia are typically marked in miles; most European races in kilometers. The distance presets (5K, 10K, half, marathon, 50K, 100K) are always exact — half marathon is 21.0975 km, marathon 42.195 km — and any custom distance works too.
Walking events. Switch the type to walking for typical walking-event distances and a slower sanity check on the target time.