How this calculator works
Lactate threshold heart rate is the intensity you can hold for roughly an hour in a race or hard effort. Coaches set cycling zones as percentages of that value because it tracks fitness better than a maximum heart rate formula. The five bands here run from 65 to 106 percent of LTHR: recovery, endurance, tempo, threshold and anaerobic. Recovery and endurance work sit below threshold, tempo is just under it, and the top two bands are for short, hard efforts.
Formula
Zone bpm = LTHR x percentage / 100. Zone 1 is 65 to 81 percent, zone 2 is 81 to 89 percent, zone 3 is 90 to 93 percent, zone 4 is 94 to 99 percent, and zone 5 is 100 to 106 percent. Zone 1 also includes anything below 65 percent.
Worked example
With an LTHR of 165 bpm, zone 1 is about 107 to 134 bpm, zone 2 is 134 to 147 bpm, zone 3 is 149 to 153 bpm, zone 4 is 155 to 163 bpm, and zone 5 is 165 to 175 bpm. An endurance ride would mostly sit in the 134 to 147 bpm band.
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Frequently asked questions
How do I find my LTHR?
A common field test is a 30-minute time trial ridden as hard as you can sustain. The average heart rate over the final 20 minutes is used as the threshold estimate. A lab test with blood lactate is more precise but not required.
Why not use 220 minus age?
That formula predicts maximum heart rate, not threshold, and it has a wide error range. Zones based on threshold reflect the intensity you can actually hold and are less sensitive to the age formula error.
Do zones change with heat or fatigue?
Heart rate drifts upward in heat and with dehydration, so the same power can land in a higher zone. Use power alongside heart rate when you have it, and retest threshold after a few months of training.