Running calculator
Interval workout calculator
Write a track session line by line — reps, distance, intensity, recovery — and get the target split for every rep, the total distance, and how long the whole set will take. Paces come from your own VDOT. Free, instant, no sign-up.
VDOT 44.5 — every rep below is priced from this race
Your session
Rep by rep
Every rep is followed by its recovery, the last one included — treat that final jog as the start of your cool-down.
One good session is easy. The coach decides how it fits the other six days.
What an interval session actually is
An interval session is repeated hard efforts separated by incomplete recovery, and the recovery is as much a part of the prescription as the reps. Run the reps too fast and the recovery stops being enough, which turns a controlled VO2 max workout into a race you did not enter. The point of writing the whole set down before you get to the track is that the last rep should look like the first one — if it does not, the session was mis-prescribed rather than bravely completed.
How this calculator works
Your race result goes through Jack Daniels' VDOT model — the same equations behind our VDOT calculator, imported here rather than copied — to get the five training intensities: easy, marathon, threshold, interval and repetition. Daniels publishes each one as a band rather than a single number (interval work sits at 95-100% of VDOT, threshold at 83-88%), so each line is prescribed at the midpoint of its band and the band itself is printed next to it. Multiply that pace by the rep distance and you have the split for every rep; add the recoveries and you have the clock time for the whole set.
How much is enough
Daniels caps interval work at roughly 8% of weekly mileage or 10 km, whichever comes first, and threshold work at about 10% — limits that exist because the fitness comes from the accumulated time near VO2 max, not from the suffering. Reps at interval pace want to last three to five minutes: shorter than that and you never reach VO2 max, longer and you cannot hold the pace. Repetition work is the opposite prescription — short, fast, and with generous recovery, because it is training your legs and not your lungs.
Running the session on the day
Warm up for at least fifteen minutes and add a few strides before the first rep, or you will spend that first rep warming up and run it too slow. Take the target as the middle of a small window and aim to finish the set on the quick end rather than starting there. If the pace falls apart two-thirds of the way through, stop the session and note it — a set you cut short is data, and a set you dragged out is just fatigue you have to pay for later in the week.