Every smartwatch shows heart rate zones, but most of them start from a generic “220 minus age” guess that can be off by 10 beats or more. Enter your age and, if you know it, your resting heart rate to get five personal training zones in beats per minute that you can copy straight into your watch.

Heart Rate Zone Calculator

How Your Heart Rate Zones Are Calculated

This calculator estimates your maximum heart rate with the Tanaka formula (208 – 0.7 x age). Research has found it more accurate across age groups than the older “220 minus age” rule, which tends to underestimate max heart rate for people over 40.

If you add your resting heart rate, the calculator switches to the Karvonen method. Instead of taking a plain percentage of your max, it works from your heart rate reserve, the gap between your resting and maximum heart rate. Two people of the same age with very different fitness levels end up with different zones, which is exactly what you want.

The best time to measure resting heart rate is right after you wake up, before coffee and before getting out of bed. Most watches and rings also report it automatically as a daily or weekly average.

The 5 Heart Rate Zones Explained

Zone % of Max (or Reserve) How It Feels Best For
Zone 1: Recovery 50-60% Very easy, full conversation Warm-ups, cooldowns, active recovery
Zone 2: Endurance 60-70% Easy, you can talk in sentences Aerobic base, fat use, long sessions
Zone 3: Aerobic 70-80% Moderate, short phrases only Tempo work, general fitness
Zone 4: Threshold 80-90% Hard, a few words at a time Intervals, raising race pace
Zone 5: Maximum 90-100% All-out, no talking Short sprints, peak power

How to Use Your Zones on a Smartwatch

Almost every major platform lets you replace the default zones with your own. On Apple Watch, open the Watch app on your iPhone, go to Workout, then Heart Rate Zones, and switch to Manual. Garmin lets you set zones by max heart rate, heart rate reserve, or lactate threshold in the user profile. Fitbit, Samsung, Google Pixel Watch, and Amazfit all support custom max heart rate or zone values in their companion apps.

Once your zones are set, turn on zone alerts for your key workouts. A gentle buzz when you drift above Zone 2 on an easy day is one of the simplest ways to stop every run from turning into a medium-hard slog.

How Accurate Is Wrist-Based Heart Rate?

Optical sensors on the wrist are reliable for steady efforts like walking, easy running, and cycling. They can lag or misread during sudden changes in intensity, heavy lifting, or activities with lots of wrist flexing. If zone accuracy matters for your training, pairing your watch with a chest strap during hard sessions gives the cleanest data.

Disclaimer: This calculator gives a general estimate based on standard heart rate formulas. It is not medical advice. Talk with a healthcare provider before making major changes to your exercise, diet, or sleep, especially if you have a health condition or take medication. Beta blockers and some other medications change heart rate response, so formula-based zones may not apply.