About the Lactate Threshold Calculator
This lactate threshold calculator turns a 30-minute solo time trial into the numbers endurance training is built around: your lactate threshold heart rate (LTHR), your threshold running pace or cycling power, and a full set of heart-rate training zones. It follows Joe Friel's widely used field test, so no lab or blood sample is needed.
It is for runners, cyclists and triathletes setting up zones on a watch or a training platform, or checking whether old zones still fit. Run the test early in a training block and repeat it every four to six weeks; your zones will follow your fitness.
In the test you race for the full 30 minutes on your own (not in a group or an actual race), press the lap button at 10 minutes, and use the average heart rate of the last 20 minutes as LTHR. Threshold pace is your average pace for the whole 30 minutes; for cycling, average power for the whole 30 minutes approximates FTP. Run and bike LTHR are usually different, so test each sport.
With the default inputs, the lactate threshold heart rate (lthr) is 168 bpm. Change any value above to recalculate instantly.
How to use the lactate threshold calculator
- 1Warm up, then time-trial alone for 30 minutes at an even, all-out effort.
- 2Press lap at 10 minutes and note the average heart rate for the last 20 minutes.
- 3Choose your sport and enter that heart rate.
- 4For running, enter the distance covered in 30 minutes; for cycling, the average power.
- 5Copy the zones into your watch or training app.
Formula and method
In Joe Friel's field test you time-trial alone for 30 minutes. Heart rate lags behind effort and is distorted by the start, so only the last 20 minutes are averaged; that average approximates the heart rate at lactate threshold. Your average pace over the full 30 minutes is your functional threshold pace, and for cycling the average power over the full 30 minutes approximates functional threshold power.
Heart-rate zones are percentages of LTHR. Running: Zone 1 under 85%, Zone 2 85–89%, Zone 3 90–94%, Zone 4 95–99%, Zone 5a 100–102%, Zone 5b 103–106%, Zone 5c over 106%. Cycling uses 81–89% for Zone 2 and 90–93% / 94–99% for Zones 3 and 4. Running pace zones are percentages of threshold pace time (Zone 2 = 114–129%). Values are rounded to whole beats per minute.
- LTHR
- Lactate threshold heart rate, bpm
- HR
- Average heart rate for the final 20 minutes of the test
- distance
- Distance covered in the full 30 minutes
Worked examples
Runner: 168 bpm, 7.2 km in 30 minutes
LTHR is the 168 bpm average from the last 20 minutes. 7.2 km in 30 minutes is 14.4 km/h, a threshold pace of 4:10 per km. Zone 2 is 85–89% of 168 (143–150 bpm) and Zone 4 is 95–99% (160–166 bpm).
Cyclist: 160 bpm and 250 W
The cycling zones are slightly lower than running: Zone 2 is 81–89% of 160 (130–142 bpm) and Zone 4 is 94–99% (150–158 bpm). The 250 W average for the full 30 minutes approximates FTP.
Runner in miles: 175 bpm, 4.5 miles
4.5 miles in 30 minutes is 9 mph, or 6:40 per mile. With LTHR at 175 bpm, Zone 2 runs from 149 to 156 bpm.
Frequently asked questions
What is lactate threshold heart rate?+
LTHR is the heart rate at which lactate starts to build up in the blood faster than it can be cleared. It is roughly the highest heart rate you can sustain for about an hour of racing, and it makes a better anchor for training zones than an age-predicted maximum.
Can I do a 20-minute test instead?+
This calculator follows Friel's 30-minute protocol, which averages heart rate over the last 20 minutes. A separate, widely used cycling convention estimates FTP as 95% of average power from a 20-minute all-out test, because shorter efforts are ridden above threshold. If you use a 20-minute test, enter that adjusted power and treat the heart rate result as approximate.
Why are my running and cycling LTHR different?+
Running uses more muscle mass and is weight-bearing, so most people reach a higher heart rate running than cycling at the same relative effort. Running LTHR is often 5–10 beats higher, so test each sport separately.
Why should I test alone and not in a race?+
Racing with others raises motivation and heart rate, which inflates the result. A solo effort gives a repeatable number you can retest every four to six weeks under the same conditions.
How is LTHR different from max heart rate?+
Max heart rate is the highest your heart can beat in an all-out effort; LTHR is typically around 85–92% of it. Zones based on LTHR better reflect your current fitness because LTHR changes with training while max heart rate barely does.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.