Your target heart rate is a percentage of your maximum heart rate, and calculating it takes just two steps: estimate your maximum heart rate using an age-based formula, then multiply by the intensity percentage that matches your workout goal. The American Heart Association recommends aiming for 50% to 70% of your max for moderate exercise and 70% to 85% for vigorous exercise.
Step 1: Estimate Your Maximum Heart Rate
The simplest and most widely used formula is 220 minus your age. If you’re 45, your estimated maximum heart rate is 175 beats per minute (bpm). This formula has been the standard since 1971, but it has a margin of error of 10 to 12 bpm in either direction, and it performs differently depending on sex.
A study of recreational marathon runners found that the 220-minus-age formula underestimated maximum heart rate by about 3 bpm in men, while overestimating it by about 5 bpm in women. A second formula, 208 minus 0.7 times your age, produced more accurate results for men (within about 1.6 bpm of their actual max) but still overestimated for women by a similar margin.
For women specifically, research has produced a dedicated formula: 206 minus 88% of your age. The standard formulas were originally developed from studies of men, and women tend to have different physiologic responses to exercise that affect peak heart rate. A 45-year-old woman using this formula would get a max of about 166 bpm, compared to 175 using the traditional calculation.
Here’s how all three compare for a 45-year-old:
- Standard (Fox): 220 − 45 = 175 bpm
- Tanaka: 208 − (0.7 × 45) = 176.5 bpm
- Gulati (women): 206 − (0.88 × 45) = 166 bpm
Step 2: Apply Your Intensity Zone
Once you have your estimated max, multiply it by the percentage range that matches your workout intensity. The American Heart Association defines two primary zones:
- Moderate intensity: 50% to 70% of maximum heart rate
- Vigorous intensity: 70% to 85% of maximum heart rate
Using the standard formula for a 45-year-old with a max of 175 bpm, moderate exercise means keeping your heart rate between 88 and 123 bpm. Vigorous exercise means 123 to 149 bpm. Brisk walking, easy cycling, and casual swimming typically fall in the moderate zone, while running, fast cycling, and competitive sports push into vigorous territory.
The Heart Rate Reserve Method
A more personalized approach factors in your resting heart rate, which reflects your baseline fitness level. This is called the Karvonen method, or heart rate reserve (HRR). The idea is simple: instead of taking a percentage of your total max, you take a percentage of the range between your resting rate and your max. Two people with the same maximum heart rate but different resting rates will get different targets, which better reflects how much room each person’s heart actually has to work harder.
The formula works like this:
Target heart rate = (maximum heart rate − resting heart rate) × desired intensity % + resting heart rate
Say you’re 45 with a resting heart rate of 65 bpm and a max of 175. Your heart rate reserve is 110 bpm (175 minus 65). For moderate exercise at 60% intensity: 110 × 0.60 + 65 = 131 bpm. For vigorous exercise at 80%: 110 × 0.80 + 65 = 153 bpm. Notice these numbers run higher than the basic percentage method, because they account for the fact that your heart is already beating 65 times per minute before you start moving.
How to Measure Your Resting Heart Rate
To use the Karvonen method, you need an accurate resting heart rate. The best time to check is first thing in the morning, right after waking up, while you’re still calm and haven’t gotten out of bed. Place two fingers on the inside of your wrist, just below the base of your thumb, or on the side of your neck. Count the beats for 15 seconds and multiply by four, or count for 30 seconds and multiply by two. Do this on a few different mornings and average the results for a more reliable number.
A typical resting heart rate for adults falls between 60 and 100 bpm, with fitter individuals often in the lower range. If yours is consistently above 100 or below 50 without a known reason, that’s worth mentioning to a healthcare provider.
Why Formulas Don’t Work for Everyone
All age-based formulas are population averages. Your actual maximum heart rate could be 10 to 12 beats higher or lower than what any formula predicts. The 2024 American Heart Association scientific statement on cardiac rehabilitation specifically cautions practitioners against relying on age-predicted maximal heart rate equations because of these wide discrepancies. For most people doing general fitness workouts, the estimates are a reasonable starting point. But if you’re recovering from a cardiac event or training at a high level, a measured maximum from a supervised exercise test is far more reliable.
Certain medications also make heart rate targets unreliable. Beta blockers slow the heart rate enough that you may never reach your calculated target, no matter how hard you push. If you take one, a perceived exertion scale is a better guide than a number. The simplest version: your workout should feel like it takes real effort, but you should still be able to carry on a conversation. If you can’t talk, you’re likely working too hard. If you can sing, you’re not working hard enough.
Putting It All Together
For a quick estimate, use 220 minus your age and multiply by 0.50 to 0.70 for moderate workouts or 0.70 to 0.85 for vigorous ones. Women may get a more accurate max from 206 minus 88% of their age. For a more personalized target, subtract your resting heart rate from your max, multiply by your desired intensity, and add your resting heart rate back in.
A chest strap heart rate monitor gives the most accurate real-time readings during exercise. Wrist-based optical sensors on fitness watches are convenient but can lag or misread during high-intensity intervals or movements with a lot of wrist motion. Whichever method you use, treat your calculated target as a guide rather than a hard rule. How your body feels during exercise, your ability to hold a conversation, and how quickly you recover afterward all matter more than hitting an exact number.