Lactate Threshold Calculator

Your lactate threshold is the hardest effort you can hold while your body still clears lactate as fast as it makes it. Push past it and lactate builds up in your blood, so the pace soon has to drop. This calculator estimates that point without a blood test, from a field test or a race you have already run.

What Lactate Threshold Measures

In a lab, you run or ride a graded test that gets harder every few minutes, and a drop of blood is tested for lactate at each stage¹. The result is a lactate curve with two turning points¹. The first threshold (LT1) is where lactate first rises above its resting level¹. The second threshold (LT2) is close to the maximal lactate steady state, the highest effort at which lactate made and lactate cleared stay in balance¹. This calculator estimates LT2. The study that tested these field methods used 4.0 mmol/L lactate as its lab threshold⁵. The result is not a VO2 max.

The Formula

LTHR = average heart rate over the last 20 minutes of a 30-minute solo time trial

Threshold pace (test) = 30 minutes ÷ distance covered

Threshold pace (race) = the speed whose oxygen cost is 88% of your VDOT

Oxygen cost (ml/kg/min) = -4.60 + 0.182258 x v + 0.000104 x v², where v is speed in meters per minute

The 30-minute test comes from coach Joe Friel, who uses the last 20 minutes for heart rate and the whole 30 minutes for pace². The race route uses the VDOT equations that Jack Daniels and Jimmy Gilbert published in 1979³.

How This Calculator Computes Your Result

Pick a route. For the 30-minute test, enter your average heart rate for the last 20 minutes, the distance you covered, or both. If you forgot to press lap at 10 minutes, enter your 30-minute average and your first 10-minute average instead. The calculator works out the last 20 minutes as (30 x full average - 10 x first 10-minute average) ÷ 20.

For the race route, choose a distance from 1 mile to the marathon (or a custom one) and enter your time. The calculator scores the race as a VDOT, then finds the pace at 88% of it. The race route gives pace only, not heart rate. Heart rate is rounded to the nearest bpm and pace to the nearest second, per km and per mile.

What Your Result Means

Each result is a training anchor, not a grade.

As a quick reference, here is the race route's threshold pace for common 5K times (our calculation with the Daniels equations³):

From a 5K, threshold pace lands about 15 to 16 seconds per km slower than race pace. From a half marathon in 1:45:00, it lands about 9 seconds per km faster than race pace. In the Daniels equations, 88% of VDOT matches the pace you could race for a little over an hour (about 67 minutes, our calculation)³.

How to Do the 30-Minute Test

Friel's test is a 30-minute time trial done alone, not with training partners and not in a race². Run it as if it were a race for the full 30 minutes². Press the lap button at 10 minutes, then read the average heart rate for the last 20 minutes². Your average pace for the whole 30 minutes is your threshold pace².

Warm up first, choose a flat route with few stops, use a chest strap if you have one, and avoid hot or windy days. Repeat the test in similar conditions so results compare.

LT1 Versus LT2

The two thresholds mark different efforts¹.

A simple talk test tracks the first threshold: the point where reciting a passage stops being comfortable sits close to the first ventilatory threshold, a breathing marker of the same shift⁴.

How Accurate Field Estimates Are

One study compared field estimates with a lab test in 27 competitive runners and triathletes⁵. On average, the 30-minute time trial matched lab threshold speed, with a typical individual error of 0.21 m/s⁵. A VDOT-based estimate also matched on average, but its typical error was about twice as large, 0.41 m/s⁵. The time trial's heart rate matched too, with a typical error of 8 bpm⁵. At a pace of 4:10 per km, 0.21 m/s is about 13 seconds per km either way (our arithmetic).

The two routes do not define threshold pace the same way. In the Daniels equations, an all-out 30-minute race is about 4 to 5% faster than the race route's threshold pace (our calculation)³. So the two routes can give different paces for the same runner, and it is best to pick one and stick with it. Labs also disagree with each other: one review found 25 different lactate threshold methods¹.