What VDOT actually is
VDOT is Jack Daniels' way of expressing fitness as a single number: the VO2max that would explain your race performance once the duration of the effort is accounted for. A 19:45 5K gives a VDOT of about 50. It is not a laboratory VO2max measurement, and it is not meant to be — it is a training tool derived from a result you can actually produce.
Why the zones are percentages of VO2max
Daniels defines training intensities as a share of VO2max, not a share of race pace. Easy running is 59–74% of VO2max, threshold 83–88%, interval 95–100%, and repetition 105–110%. Because the relationship between pace and oxygen cost is curved, a fixed percentage of race pace would drift out of the intended zone as fitness changes. The calculator inverts the oxygen-cost equation for each percentage, which is why the easy range is so wide.
How to use the zones
Run most miles at E pace — the slow end of the range is not laziness, it is the point. Add one or two quality sessions a week at T or I pace, and keep R for short speed work when sharpening for a race. The equivalent-times table is a sanity check: if your VDOT from a 5K implies a marathon two minutes faster than you have run, the marathon is the place to look, not the calculator.
Frequently Asked Questions
Is VDOT the same as VO2max?
No. It is a pseudo-VO2max derived from race performance, adjusted for how long the race lasted. Lab VO2max and VDOT usually differ by a few points.
Which race should I use?
A recent race of 5K to half marathon, run all out. Very long races understate VDOT because fuelling and pacing, not fitness, become the limit.
Why is my easy pace so slow?
Easy pace is 59–74% of VO2max, which feels slow by design. Most runners run their easy days too fast, which compromises the quality sessions that follow.
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