How Our Running Calculators Work

Most calculators use direct time, distance, and speed arithmetic. Inputs are processed in your browser. Here are the main calculations and assumptions used in this version of Finish Line Labs.

Pace and finish time

Pace = elapsed time ÷ distance. The pace calculator converts the entered time and distance to seconds per mile and kilometer. The finish-time calculator multiplies the selected distance by the target pace after converting between miles and kilometers using 1 mile = 1.609344 kilometers.

Race-time predictions

The race predictor uses the Riegel-style power equation: predicted time = known time × (target distance ÷ known distance)^1.06. The exponent is an approximation. A prediction extrapolates from one result; it does not measure endurance, training volume, course conditions, fueling, or current fitness at another distance. Read the limits of race predictions.

Race splits and negative splits

Even splits divide total target time in proportion to distance. The negative-split calculator divides the total time into two halves using the selected time difference, with the second half faster. Real courses and pacing strategies may not divide evenly.

Treadmill speed and interval time

At a treadmill speed of v miles per hour, pace is 3,600 ÷ v seconds per mile. Interval totals add the entered fast-running time and planned recovery time. Recovery time is counted between repetitions, so a workout with n repetitions has n − 1 recovery periods.

Heart-rate zones

The heart-rate calculator displays five bands: 50–60%, 60–70%, 70–80%, 80–90%, and 90–100%. It compares two common arithmetic methods: percentage of the entered maximum heart rate, and heart-rate reserve (resting heart rate + percentage × [maximum − resting]). These are estimates, not individualized medical or training recommendations. Maximum heart rate can be difficult to estimate accurately.

Check the result against reality

Use estimates as planning aids. Verify race distances, watch settings, course conditions, and any result that matters to you. Calculator outputs are not guarantees or medical advice. For additional guidance, see the race-day pacing checklist and how to choose training paces.