Calculator
Example data table
| Session | Interval | Work Time | Rest | Repeats | Total Work | Total Rest |
|---|---|---|---|---|---|---|
| Track repeats | 400 m | 1:40 | 1:00 | 6 | 10:00 | 5:00 |
| Tempo blocks | 1 km | 4:10 | 1:30 | 4 | 16:40 | 4:30 |
| Hill surges | 0.25 mi | 1:50 | 1:10 | 8 | 14:40 | 8:10 |
These examples show common inputs you can test inside the calculator.
Formula used
- Distance conversion: meters = distance × unit factor.
- Pace per km: pacekm (sec/km) = time (sec) ÷ distance (km).
- Pace per mile: pacemi (sec/mi) = time (sec) ÷ distance (miles).
- Speed: km/h = distance (km) ÷ time (hours).
- Total work time: work time × repeats.
- Total rest time: rest time × rest segments.
- Total session time: work + rest + warmup + cooldown (planner mode).
How to use this calculator
- Pick a mode: plan a full session, compute pace, or compute time.
- Enter your interval distance, unit, and number of repeats.
- Provide either work time per interval or a target pace.
- Add rest time and choose how rest is applied.
- For session planning, include warmup and cooldown times.
- Optionally add a baseline race time to compare pacing.
- Press Calculate to view results above the form.
- Use the download buttons to export CSV or PDF.
Why pacing matters
Intervals work best when effort stays measurable and repeatable. A 400 m repeat in 1:40 equals 4:10 per km, so small drift is obvious. If your sixth repeat slips to 1:48, pace becomes 4:30 per km and fatigue is rising. Tracking pace protects quality, helps avoid chasing the clock, and supports progression across weeks.
How the calculator computes
The calculator converts distance to meters, then converts time to seconds. Pace per kilometer equals seconds divided by kilometers; pace per mile uses miles from 1609.344 meters. Speed uses distance per hour, so 400 m in 100 seconds equals 14.40 km/h. With repeats, total work time is work seconds times intervals. To compare different interval formats, keep distance constant and change time, or keep time constant and change distance. For example, 800 m in 3:20 matches 4:10 per km, while 600 m in 2:30 matches 4:10 per km too.
Rest density and session load
Recovery changes the training signal as much as speed. Six repeats with 60 seconds rest between creates five rest blocks, adding 300 seconds. If rest is applied after every interval, rest becomes 360 seconds, increasing session time without changing pace. The chart separates work and rest so you can see density, not only totals.
Baseline comparisons for control
Optional baseline inputs create a practical reference. A 22:00 5K implies 4:24 per km. If intervals compute to 4:10 per km, that is about 5.3% faster than baseline pace. Use the percentage as a guide, not a rule, because terrain, temperature, and fitness trend can shift effort on the day.
Reviewing splits and exports
The splits table repeats the same work target when time is fixed, but cumulative time highlights how long the session actually takes. Exporting CSV supports quick analysis, like checking weekly volume or comparing rest ratios. The PDF version is useful for printing a track plan or sharing a session with a coach.
Practical interval examples
For 1 km repeats, try 4 × 1 km at 4:10 with 1:30 recovery; work equals 16:40 and rest equals 4:30. For speed, try 8 × 200 m at 0:45 with 0:60 rest; work equals 6:00 and rest equals 7:00. Adjust repeats first, then pace, to progress safely.
FAQs
1) What is interval pace?
Interval pace is the pace calculated from one work segment only. It ignores recovery, so you can compare repeats consistently. Session pace averages work plus rest, and may also include warmup and cooldown in planning mode.
2) Should I choose per kilometer or per mile?
Use the unit that matches your training logs and race goals. The calculator shows both, but target pace input uses your chosen unit. Consistency makes comparisons across workouts and weeks more meaningful.
3) How should I set rest time?
Start with enough recovery to keep the last repeat within your target range. Shorter rest increases density and stress; longer rest improves speed quality. If form breaks or pace drops sharply, increase rest or reduce repeats.
4) Why does total time change with rest settings?
Rest can be counted between intervals only, or after every interval. Between-only uses repeats minus one rest blocks; after-each uses repeats rest blocks. That difference changes total session time, even when work pace stays unchanged.
5) Can this be used for treadmill or indoor training?
Yes. Enter the distance you cover per interval and the time you hold that effort. For treadmill intervals, distance can be computed from speed and time externally, then used here to generate pace, totals, and exports.
6) How should I interpret baseline comparison?
Baseline is a reference pace derived from your race time and distance. A positive percentage means your interval pace is faster than baseline. Use it to sanity-check intensity, not to force a specific number on tough days.