What this calculator does
Strap on a chest belt or a watch and you’ll see one number jumping around: your heart rate. On its own it means little. The trick is knowing which beats per minute count as “easy” for you and which mean you’re redlining. That’s what zones are for, and this is where you get yours.
Punch in your age. The calculator estimates your maximum heart rate, then carves it into five training zones, each shown as a real BPM range you can actually read off a monitor. Got your resting heart rate handy? Toggle Karvonen on and the zones sharpen to your fitness instead of a generic curve.
How the numbers come out
Max heart rate is the ceiling, the fastest your heart will beat. You can’t train it higher, and it drifts down a beat or so a year as you age. Two formulas estimate it from age:
- 220 minus your age. The classic. A 40-year-old lands at 180. It’s everywhere because it’s easy, not because it’s precise.
- Tanaka: 208 minus 0.7 times age. Newer, built from a 2001 meta-analysis, and it fits people over 40 noticeably better. Same 40-year-old comes out at 180 too, but a 60-year-old gets 166 instead of 160.
Once there’s a max, the five zones fall out as percentages: 50-60, 60-70, 70-80, 80-90, and 90-100 percent. By default each zone is just that slice of your max. Simple.
Karvonen does something smarter. It uses heart rate reserve, the gap between your max and your resting pulse. The target becomes (max minus rest) times intensity, plus rest. Because a fit person has a lower resting heart rate, their reserve is wider and the zones spread out to match. A couch potato and a marathoner with the same age get different Zone 2 numbers, which is the whole point.
What each zone is good for
Zone 1 is barely-working territory: warm-ups, cool-downs, recovery strolls. Zone 2 is the one endurance coaches obsess over. Long, conversational, fat-burning effort that builds your aerobic base. You should be able to talk in full sentences.
Zone 3 is moderate cardio, the “comfortably hard” middle. Zone 4 brushes your lactate threshold, where breathing gets ragged and you can only gasp a few words. Zone 5 is the top floor: short, brutal intervals, 90 percent and up, sustainable for seconds to a couple minutes. Most people spend far too much time in the murky Zone 3 and not enough at the easy and hard ends.
Common questions
How accurate is the estimated max? It’s a ballpark. Age-based formulas carry a standard deviation around 10 to 12 bpm, so your true max could be well above or below the number. A graded treadmill or bike test, ideally supervised, is the only way to pin it down.
Should I use Karvonen or plain percent of max? Karvonen if you know your resting heart rate, since it personalizes the zones. Take your resting pulse first thing in the morning before you get out of bed for the cleanest reading. Without it, plain percent is fine to start.
Why is my Zone 2 higher with Karvonen turned on? Because Karvonen adds your resting rate into every target. A resting pulse of 60 lifts the whole range up compared to a flat percentage of max, which assumes you start from zero.
Does a beta-blocker change this? Yep, a lot. Medications that slow your heart, beta-blockers especially, push your max and your zones well below any formula. If you’re on one, ask your doctor for numbers based on a real test.
Is 220 minus age outdated? It’s not wrong so much as rough, and it overestimates max for older adults. Tanaka is the better pick past 40. Both are guesses, so treat either as a starting line, not gospel.