Race split calculator
Plan mile or kilometer splits from a finish target or moving pace, with an explicit stop allowance and your choice of first-half time share.
Moving pace versus elapsed finish time
Your elapsed time includes stops. For a 10K target of 50:00 with 2:00 stopped, you have 48:00 to move: an average moving pace of 4:48/km. Holding 5:00/km while moving would finish in 52:00 after those stops. The stop allowance is a budget you supply, not a recommendation.
How the two-half strategy works
With a 50% first-half share, both halves take the same moving time. With 52%, the first half uses 52% of moving time and the second uses 48%, giving a faster second half. In the example, that is 24:57.6 for the first 5K and 23:02.4 for the second. Pace is constant within each half; this does not model a gradual acceleration.
The table includes halfway even when it falls between your chosen mile or kilometer marks, plus the exact final partial distance. Moving time at a checkpoint comes from distance traveled within each half. Budgeted elapsed time adds the same fraction of your stop allowance as the fraction of race distance completed. Actual stops at specific aid stations can make your clock differ from that evenly spread budget.
Units, precision and limits
Distance, pace and split-table units are independent. Changing a distance or pace unit converts the existing value. Race buttons set distance in kilometers. The NIST unit reference gives one international mile as exactly 1,609.344 meters. Marathon and half-marathon buttons use 42.195 km and 21.0975 km.
Enter times as m:ss or h:mm:ss, including 0:00 for no stops. Displayed times round to tenths of a second; cumulative times use unrounded calculations, so adding rounded pieces may differ slightly. CSV calculation rows retain numeric precision. Distance is limited to 1,000 selected units, the first-half share to 40–60%, and elapsed plans to seven days. These are tool limits, not training guidance.
For walk breaks, use the run/walk finish-time calculator. To turn a chosen pace into repeated track efforts, use the track interval calculator. This page provides arithmetic, not a prediction that you can sustain the entered pace.