Why "220 minus your age" is only a rough guess

Your maximum heart rate is the highest number of beats per minute your heart can reach when you push as hard as you possibly can. Many heart-rate zones, on watches and in training plans, are drawn as percentages of that number, so it matters that the number is sensible.

The famous shortcut is 220 minus your age. It is easy to remember, and it was never meant to be exact. Later research looked at many more people and produced other formulas, such as 208 minus 0.7 times your age (often called the Tanaka formula) and 207 minus 0.7 times your age (the Gellish formula). The formulas disagree with each other, and even the best of them is an average: real people of the same age can differ from it by about ten beats per minute or more in either direction.

What the spread means in practice

Say you are 35. The formulas land between about 183 and 185 beats per minute, but your own true maximum could comfortably be 175 or 195. If you set zones as a percentage of the wrong number, "easy" could feel hard, or "hard" could be too gentle.

That is why the guess is best used as a starting point, not a verdict. Some people notice their watch showing numbers above the formula. That is not a sign something is wrong; it just means the average does not describe them exactly.

Better than a formula: use effort

For a beginner, you do not need an exact maximum to train well. Two simple checks work with any heart rate or none at all:

• The talk test. If you can speak in full sentences, you are in easy territory. If you can only manage a few words at a time, you are working hard.
• A 1–10 effort scale. Most of your cardio should feel like a 3 to 5 out of 10, meaning comfortable and repeatable.

If you do use a heart-rate watch or strap, treat the zones as a rough guide and let the way you feel overrule the number when they disagree. Our guide to zone 2 shows how the talk test lines up with it.

Who should not go looking for a true maximum

Measuring your real maximum means an all-out effort. It is not a good idea to try this alone as a new exerciser, and it is not for anyone with a heart condition, chest pain, dizziness on exertion, or who has been told to be careful with exercise. If any of that sounds like you, or you are unsure, check with your doctor before pushing hard. Some medicines, such as beta blockers, also lower heart rate, which makes every formula here unreliable for you.

The short version

Pick any of the formulas as a rough starting point, remember that the real answer could be around ten beats either side, and let your breathing and effort decide how hard a session really is. A number that is a little off will not hurt your training; trusting it over your own body can.