Heart rate zones turn one number, your pulse, into a training plan. Instead of guessing whether a session was easy or hard, you compare your heart rate with five zones, each with its own purpose. This calculator builds your personal five-zone table from your age and resting heart rate, using two well-known formulas, and explains what each zone trains and what kind of session belongs in it. That turns a heart rate monitor from a gadget into a coach.
The first step is your maximum heart rate, the fastest your heart can beat. The classic estimate is 220 minus your age, so a 35-year-old gets 185 beats per minute. The Tanaka formula, 208 minus 0.7 times your age, gives 184 for the same person, and researchers consider it slightly more accurate for older adults. Neither formula is exact: your true maximum can differ by 10 to 20 beats, which is why a laboratory test or a hard all-out effort gives a better number if you ever measure one.
The second step is the Karvonen method, which uses your resting heart rate to personalise the zones. Heart rate reserve is your maximum minus your resting rate, and a zone is a percentage of that reserve added back to your resting rate. A fit person with a resting rate of 50 gets different zone boundaries from an unfit person of the same age with a resting rate of 75, even though their maximums match. That is the point: Karvonen zones reflect your fitness, while plain percentages of maximum treat everyone of the same age alike.
Here is a worked example. A 35-year-old with a resting rate of 60 has a classic maximum of 185 and a reserve of 125. Zone 1, 50 to 60 percent, is 123 to 135 beats per minute by Karvonen. Zone 2, 60 to 70 percent, is 135 to 148. Zone 3, 70 to 80 percent, is 148 to 160. Zone 4, 80 to 90 percent, is 160 to 173. Zone 5, 90 to 100 percent, is 173 to 185. The calculator shows all five at once, so you can write them on a card or save them in your watch before your next session.
Each zone has a distinct job. Zone 1 is recovery: easy walking, gentle spinning, or a warm-up, where you can talk in full sentences and feel almost no strain. Zone 2 is the aerobic base: long, comfortable sessions that build endurance and fat burning, and most of your weekly training should live here. Zone 3 is tempo: comfortably hard, where talking becomes broken sentences and you can hold the effort for 20 to 40 minutes. Zone 4 is threshold: hard and sustained, near the point where lactate builds faster than you clear it. Zone 5 is maximum: very hard intervals of 30 seconds to 3 minutes, with full recovery between them.
How much time belongs in each zone depends on your goal, but a common pattern for endurance athletes is about 80 percent of training time in zones 1 and 2, and about 20 percent in zones 4 and 5, with zone 3 used sparingly. Beginners should spend even more time easy: easy training builds the base that later makes hard training useful, while too much hard training too soon leads to fatigue, illness, or injury. If your heart rate drifts above the planned zone on a long session, slow down; holding the zone matters more than holding a pace.
This tool is an educational estimator only, never medical advice. The formulas are population averages, and medicines, illness, heat, altitude, caffeine, and poor sleep all shift your heart rate. Some heart conditions and medicines, such as beta blockers, make heart rate zones unreliable or unsafe to chase. If you have a heart condition, take heart medicine, feel chest pain, dizziness, or unusual breathlessness during exercise, stop and seek professional medical advice. Real training and medical decisions need a professional, not a web calculator.
To use the tool well, measure your resting heart rate first thing in the morning, before coffee, for several days, and use the average. Pick the Tanaka formula if you are over 40, and the Karvonen method if you know your resting rate. Then set the five zones in your watch or write them down, and check them during sessions rather than afterwards. Over weeks, your resting rate should fall and your pace at the same heart rate should rise, which is the clearest sign that your training is working.