Heart Rate Zone Calculator

Not very. It was never derived from data — it turned up in a 1971 review as a rough summary of a scatter of studies and stuck. It reads low with advancing age, which pushes older people into zones harder than the label suggests. Tanaka’s 208 − 0.7 × age fits measured data considerably better.

It works from heart rate reserve, your maximum minus your resting rate, and adds a share of that reserve back on top of the resting figure. It lands higher than a plain percentage of maximum at every zone, and it accounts for the fact that someone with a low resting rate has more range to work across.

Around any age-based formula the scatter between individuals is roughly ten beats either side, and plenty of people sit further out than that. Ten beats is a whole zone. The highest rate you have genuinely seen on a chest strap during an all-out effort beats every equation on the page.

Wrist optical sensors lose the pulse during intervals, in the cold, and whenever you grip something hard, and they sometimes lock on to the cadence of your steps instead. A reading sitting suspiciously flat during hard work is usually the watch. A chest strap is far more reliable for zone training.

Beta blockers and several other medicines lower both resting and maximum heart rate, so zones built from age alone will not describe you. That is a conversation for whoever prescribed it. Nothing on this page is a reason to change anything you have been prescribed, and it cannot account for the effect.

Yes. There is no account, no daily cap, no file-size tier and no watermark, because there is no server cost to recover. The site is funded by clearly disclosed partner recommendations on the Partners page, never by metering the tools.

No. Everything is processed by JavaScript running in your browser, on your device. You can verify it: open your browser's developer tools, switch to the Network tab, and use the tool. You will see no request carrying your data — because there is nowhere for it to go.