What 220 − age is
It is a 1970s-era estimate of maximum heart rate. Real maxima vary by 10–20 beats in either direction. Zone percentages piled on top of a shaky maximum are therefore also shaky. Use them to understand what a watch is trying to say, not to punish a Tuesday walk.
Zone 2 chatter online is louder than the evidence that every adult must live there. Walking that you can still talk through remains a legitimate session, especially if you are also using the knee, back, or balance pages.
Worked example
Age 50 → estimated max 170. Fifty to sixty percent is about 85–102 bpm. That is an easy walk for many people. Eighty percent is 136. If a watch screams “peak” on a flight of stairs, believe the stairs and your breathing more than the badge.
Read the longer note on heart rate, sleep, and wearables before you buy another strap. Blood pressure still needs a cuff: home BP.
Frequently asked
Does the heart-rate calculator store what I type?
No. The arithmetic runs in your browser. See the privacy page.
Is this medical advice?
No. Read the medical disclaimer. Take unusual results to a clinician.
Should children use this?
No. These tools are written for adults.
How does this sit next to BMI?
Use the BMI calculator as a size snapshot, then return here for the question this page actually answers.
What should I read after the number?
Food: meal framework. Joints: knees or back. Metrics: adult indicators.
Formulas are named on the page. They are planning maths, not clinic devices.
Using the result in a normal week
Write the figure once. Do not recalculate after every meal. Recalculate when weight has changed by several kilograms, when a clinician has changed a medicine that affects weight or heart rate, or when your job has become much more or much less physical. Daily recalculation is how a useful tool becomes noise.
Food still comes from the meal framework, the foods list, and the dinner templates in the journal. Movement still comes from walking and from the mobility articles when a joint is the limit. Metrics still come from waist, blood pressure, and sleep on the adult-indicator pages.
If the result looks extreme, assume the inputs or the equation limits before you assume your body is extreme. Heights typed in the wrong unit are the usual villains. Then talk to a person who can examine you.
Keep the same units you used last time. Measure height once against a wall and write it in the notebook you already keep for waist, morning weight, and walks. Consistency beats precision theatre.
Using the result in a normal week
Write the figure once. Do not recalculate after every meal. Recalculate when weight has changed by several kilograms, when a clinician has changed a medicine that affects weight or heart rate, or when your job has become much more or much less physical. Daily recalculation is how a useful tool becomes noise.
Food still comes from the meal framework, the foods list, and the dinner templates. Movement still comes from walking and from the mobility articles when a joint is the limit. Metrics still come from waist, blood pressure, and sleep — see adult indicators and home blood pressure.
Shortcuts that promise to replace this work are collected in why crash diets fail and teas, wraps, and shortcuts. Read those if the reason you opened a calculator was a product promise rather than a planning question.
If the result looks extreme, assume the inputs or the equation limits before you assume your body is extreme. Heights under 140 cm or weights typed in the wrong unit are the usual villains. Then talk to a person who can examine you. A second calculator tab is not that person.
Keep the same units you used last time. Mixing pounds and kilograms, or inches and centimetres, is the most common way to get a theatrical result. When in doubt, measure height once against a wall and write it in the notebook you already keep for waist, morning weight, and walks. Consistency beats precision theatre.