Interval Training Calculator

Target Work Pace is your Current Easy Pace (entered as minutes and seconds per mile) multiplied by a per-second-per-meter Work Pace Factor that depends on Session Type: 0.9x for Threshold/Tempo (a comfortably-hard effort a bit faster than easy pace), 0.86x for VO2max Intervals (a hard effort closer to 5K-race intensity), or 0.82x for Speed/Repetition (the fastest of the three, meant for short, all-out reps). Because a lower multiplier on time-per-distance means a faster pace, Speed sessions always compute the fastest Target Work Pace, VO2max the second-fastest, and Threshold the slowest -- matching how those training zones are used in practice. Rest Duration is the Work Interval Duration multiplied by a Session-Type-specific work:rest ratio -- 1:0.25 for Threshold (short recovery), 1:1 for VO2max (equal work and rest), or 1:2 for Speed (long recovery relative to a short, very fast rep) -- reflecting that the harder and shorter the effort, the more recovery it needs between reps.

Total Interval Distance is simply Interval Distance multiplied by Number of Intervals; it does not depend on your pace inputs or your Session Type selection at all, so changing either of those reshapes your target paces and rest durations without changing how far the workout covers in total. Full Session (incl. warmup/cooldown) adds a fixed 20 minutes (10 minutes warmup plus 10 minutes cooldown) on top of the computed work-and-rest total, a common recommendation for structured interval sessions to reduce injury risk and prime interval quality.