Heart rate zone calculator

Your maximum heart rate and the five training zones underneath it. Add your resting heart rate and the zones get personalised rather than assumed.

Milo

Age

Resting HR (optional)

Your zones will appear here.

How this is worked out

The maximum uses the Tanaka formula, not the familiar 220 minus age:

max HR = 211 − 0.64 × age

That old 220 rule was never research, just a line drawn through some scattered data in the 1970s. It overestimates for younger people and underestimates for older ones, often by close to a decade’s worth of beats. Tanaka came from a proper meta-analysis and fits considerably better.

Give it a resting heart rate and it switches to the Karvonen method, which works from heart rate RESERVE, the gap between resting and maximum. That matters because two 40-year-olds with resting rates of 45 and 75 shouldn’t train to the same zone numbers, and percentage-of-max pretends they should.

Milo can read your resting heart rate straight from Apple Health or Health Connect, so the number stays current as your fitness changes.

The number is the easy part

Any calculator can hand you a figure. The hard bit is the next three months: eating roughly to it, noticing when it stops working, and changing it. Milo is a coach you text like a friend. You log what you ate in a sentence, and it learns your patterns, notices when your weight stalls, and adjusts the target from what you actually did rather than from a formula.

See how Milo works

Common questions

Which zone should I train in?

Most of your easy work belongs in zone 2, where you can still hold a conversation. It’s the least exciting and the most useful. Add a smaller amount of hard work in zones 4 and 5. The common mistake is living in zone 3, too hard to recover from and too easy to drive real adaptation.

How accurate is a formula-based maximum?

It’s a population average, and individuals scatter around it by 10 to 12 beats either way. If you’ve ever seen a genuinely higher number on a watch during an all-out effort, trust that over the formula.

How do I find my true resting heart rate?

First thing in the morning, before you get up, or let a watch measure it overnight. A resting rate that climbs several beats above your normal for a few days is a decent early sign of fatigue or illness.

Does a lower resting heart rate mean fitter?

Broadly, yes, within yourself. As aerobic fitness improves, resting rate tends to fall, because the heart moves more blood per beat. Comparing your number against someone else’s is much less meaningful, since genetics set a lot of it.

Other calculators

One rep max calculator — Your estimated 1RM from a working set, plus a full rep-max table.
Calories burned calculator — What a session actually costs, by activity, weight and time.
Running pace calculator — Pace, speed and what it projects over 5k, 10k and a marathon.
TDEE calculator — How many calories you burn in a day, and what to eat for your goal.
Calorie deficit calculator — How long a given deficit takes to reach your goal weight.

These are estimates from population averages, not measurements of you. Individual metabolism varies by roughly ±10% around any formula. Nothing here is medical advice — if you have a health condition, are pregnant, or are under 18, talk to a healthcare professional before changing how you eat or train.