Maximum heart rate and the zones
Training zones are percentages of your maximum heart rate. The simplest estimate of that maximum is 220 minus your age; the Tanaka formula, 208 − 0.7 × age, fits measured data better, especially over 40. Both are population averages: real maxima vary by 10–12 bpm either way at any age, so a measured max from a hard race or a fitness test is worth entering if you have one.
Without a resting heart rate, the moderate (50–70% of max) and vigorous (70–85% of max) ranges are the American Heart Association's, which recommends at least 150 minutes a week of moderate or 75 minutes of vigorous activity.
With a resting heart rate, the calculator switches to a separate method: the Karvonen heart-rate-reserve formula with the American College of Sports Medicine's ranges, moderate 40–59% and vigorous 60–89% of reserve (ACSM's Guidelines for Exercise Testing and Prescription, 11th edition). At age 40 with a resting pulse of 60, max is 180 and reserve is 120, so moderate is 60 + 0.40 × 120 = 108 to 60 + 0.59 × 120 = 131 bpm and vigorous 132–167 bpm. The two authorities' percentages are never mixed: AHA percentages apply to maximum heart rate, ACSM's to heart-rate reserve.
| Age | Max HR | Moderate (AHA 50–70%) | Vigorous (AHA 70–85%) |
|---|---|---|---|
| 20 | 200 | 100–140 | 140–170 |
| 30 | 190 | 95–133 | 133–162 |
| 40 | 180 | 90–126 | 126–153 |
| 50 | 170 | 85–119 | 119–144 |
| 60 | 160 | 80–112 | 112–136 |
| 70 | 150 | 75–105 | 105–128 |
The five zones
Separately from the guideline ranges above, most training systems divide effort into five zones; these are a coaching convention rather than an AHA or ACSM guideline. Zone 2 — easy enough to hold a conversation — is where endurance athletes spend most of their time, building aerobic capacity and fat-burning efficiency. Zones 4 and 5 are for intervals. Zone 3 is the 'grey zone' that feels productive but is neither easy enough to recover from quickly nor hard enough to drive top-end fitness; polarised programs largely avoid it.
| Zone | % of max | Feel | Purpose |
|---|---|---|---|
| Zone 1 | 50–60% | Very light | Warm-up, cool-down, recovery walks |
| Zone 2 | 60–70% | Light | Long easy runs and rides; builds aerobic base |
| Zone 3 | 70–80% | Moderate | Tempo; 'comfortably hard' |
| Zone 4 | 80–90% | Hard | Threshold intervals; talking is difficult |
| Zone 5 | 90–100% | Maximum | Short intervals and sprints; 30 s – 3 min |
The Karvonen method
Percent-of-max zones ignore fitness: a trained athlete with a resting pulse of 45 and an untrained person at 80 with the same max get identical zones, though the same heart rate means very different effort for each. Karvonen's method fixes this by working with heart-rate reserve (max minus resting): target = resting + % × reserve. The zones shift upward for fitter people. Enter your resting heart rate — measured lying down before getting up — and the calculator switches methods: the five zones are then taken as percentages of reserve, and the moderate and vigorous ranges become ACSM's 40–59% and 60–89% of reserve.
| Zone | % of max | Karvonen |
|---|---|---|
| Zone 1 (50–60%) | 92–111 | 122–135 |
| Zone 2 (60–70%) | 111–130 | 135–148 |
| Zone 3 (70–80%) | 130–148 | 148–160 |
| Zone 4 (80–90%) | 148–166 | 160–172 |
| Zone 5 (90–100%) | 166–185 | 172–185 |
Estimating maximum heart rate
Several formulas exist; all are approximate. 220 − age is the oldest and simplest and overestimates for older adults. Tanaka (2001) and Nes (2013, 211 − 0.64 × age) come from larger, more recent samples. The differences are within the error of any of them. A field test — after a thorough warm-up, three minutes as hard as you can sustain, then a sprint finish — gives a personal number, but should only be attempted if you are healthy and used to hard exercise.
| Age | 220 − age | Tanaka | Nes |
|---|---|---|---|
| 20 | 200 | 194 | 198 |
| 30 | 190 | 187 | 192 |
| 40 | 180 | 180 | 185 |
| 50 | 170 | 173 | 179 |
| 60 | 160 | 166 | 173 |
| 70 | 150 | 159 | 166 |
| 80 | 140 | 152 | 160 |
Fat burning and heart rate
The 'fat-burning zone' (roughly zone 2) is the intensity at which the largest share of energy comes from fat. It is real, but the total energy burned per minute is lower than at higher intensities, and over a day the body balances fuels anyway; for weight loss, total energy expenditure matters more than the fuel mix during exercise. Zone 2's real value is that it can be sustained for long periods and recovered from easily, which is what builds an aerobic base.
Using heart rate in practice
Heart rate lags effort by a minute or two and drifts upward in heat, dehydration and fatigue, so it suits steady efforts better than short intervals, where pace or power is a better guide. Beta-blockers and some other medications lower maximum heart rate substantially; caffeine and stress raise resting heart rate. Wrist optical sensors are reasonably accurate at steady effort and unreliable during intervals; a chest strap is better for zone work. Whatever the numbers say, effort that feels 'easy', 'comfortably hard' and 'very hard' maps well onto zones 2, 3–4 and 5.