A good heart rate during exercise falls between 50% and 85% of your maximum heart rate, depending on how hard you’re pushing. For a 40-year-old, that translates roughly to 90 to 153 beats per minute. Where you should land within that range depends on your fitness level and what you’re trying to accomplish.
How to Find Your Maximum Heart Rate
Every target heart rate starts with one number: your estimated maximum heart rate. The simplest formula is 220 minus your age. If you’re 35, your estimated max is 185 beats per minute. A slightly more refined formula, developed by researcher Hirofumi Tanaka, calculates it as 208 minus 0.7 times your age, which gives a 35-year-old an estimated max of 183.5. Both are approximations, but they’re close enough to build your training zones from.
Here’s what those numbers look like across several ages using the 220-minus-age formula:
- Age 25: estimated max of 195 bpm
- Age 35: estimated max of 185 bpm
- Age 45: estimated max of 175 bpm
- Age 55: estimated max of 165 bpm
- Age 65: estimated max of 155 bpm
Target Zones for Different Workout Intensities
Moderate-intensity exercise, like brisk walking, steady cycling, or an easy jog, puts you at 50% to about 70% of your max. For a 45-year-old with a max of 175, that’s roughly 88 to 123 bpm. This is where most general health benefits happen: lower blood pressure, better blood sugar control, improved mood. If you can carry on a conversation but feel slightly winded, you’re likely in this zone.
Vigorous-intensity exercise, like running, fast cycling, or a challenging group fitness class, pushes you to 70% to about 85% of your max. That same 45-year-old would aim for 123 to 149 bpm. You’ll be breathing hard enough that speaking in full sentences becomes difficult. This zone builds cardiovascular endurance faster and burns more calories per minute.
High-intensity interval training (HIIT) asks you to spike even higher, typically 85% to 95% of your max, but only in short bursts. A well-studied HIIT format alternates four minutes at 85% to 95% of max with three minutes of recovery at around 60% of max, repeated four times. That recovery period matters just as much as the hard intervals.
What Your Body Burns at Different Intensities
At lower intensities (roughly zones 1 and 2 on a five-zone scale), your body relies primarily on fat for fuel. It breaks down fat through a slower metabolic process that works well when oxygen supply is plentiful. This is why you’ll hear the phrase “fat-burning zone” applied to easier efforts.
As intensity climbs into zones 3 through 5, your body shifts toward burning carbohydrates because it can extract energy from sugar faster than from fat. You do burn a bit less fat per minute at higher intensities, but you burn significantly more total calories. For weight management, the total calorie burn usually matters more than the fuel source. For building endurance and aerobic fitness, spending time in zone 2 (light effort, roughly 60% to 70% of max) has its own distinct benefits. A mix of both intensities across your week covers the most ground.
A More Personalized Calculation
The basic percentage-of-max approach treats everyone the same, but your resting heart rate tells a more complete story. Someone with a resting heart rate of 55 has a larger “usable range” of heart rate than someone resting at 80, even if they’re the same age. The Karvonen method accounts for this by using your heart rate reserve: your maximum heart rate minus your resting heart rate.
To calculate a target: multiply your heart rate reserve by the percentage you want, then add your resting heart rate back. For example, a 40-year-old with a resting heart rate of 60 and a max of 180 has a reserve of 120. To find a 70% target: 120 × 0.70 = 84, plus 60 = 144 bpm. This tends to give a more accurate picture of actual effort, especially if you’re very fit or relatively new to exercise.
To get your resting heart rate, check your pulse first thing in the morning before getting out of bed. Count for 60 seconds on a few different days and average the results.
Factors That Shift Your Heart Rate
Your heart rate during the same workout can vary by 10 to 20 beats depending on conditions. Heat and humidity force your heart to work harder because blood gets diverted to your skin for cooling. Dehydration reduces blood volume, so your heart compensates by beating faster to deliver the same amount of oxygen. Caffeine, poor sleep, and stress all nudge your resting and exercise heart rates upward.
Certain medications change the equation entirely. Beta-blockers, commonly prescribed for high blood pressure, directly limit how fast your heart can beat. If you take one, the standard formulas will overestimate your target zones, sometimes dramatically. Diuretics can contribute to dehydration and electrolyte shifts that also affect heart rate response. If you’re on either type of medication, a perceived-exertion approach (rating how hard you feel you’re working on a 1-to-10 scale) is often more reliable than chasing a specific number.
How Fast Your Heart Rate Should Drop After Exercise
One of the most useful numbers isn’t your peak heart rate during a workout. It’s how quickly your heart rate falls once you stop. A healthy drop is 18 beats or more in the first minute after you stop exercising. This measurement, called heart rate recovery, reflects how well your nervous system shifts from “go” mode back to rest. Over weeks of consistent training, you should see this number improve, meaning your heart rate drops faster.
Most of the meaningful recovery happens in the first two to five minutes. If your heart rate is still elevated and you feel symptoms like pounding palpitations, chest pain, lightheadedness, or near-fainting after you’ve cooled down, that’s worth paying attention to. Brief spikes during hard effort are expected, but a heart that stays racing or flutters irregularly after you’ve stopped is sending a different signal.
Putting It All Together
For most people doing general fitness workouts, staying between 50% and 85% of your max heart rate is the practical sweet spot. If you’re just starting out, aim for the lower half of that range (50% to 70%) and build up over several weeks. If you’re training for performance or doing structured interval work, you’ll intentionally push into the 85% to 95% range for short periods. The key is that the “right” heart rate matches your goal for that specific session: easy days should feel easy, hard days should feel hard, and your body should recover predictably between them.
A chest strap heart rate monitor gives the most accurate real-time readings. Wrist-based optical sensors on smartwatches have improved significantly but can lag during rapid changes in intensity or read inaccurately if the band is too loose. Either way, tracking your heart rate over time gives you something more valuable than any single workout number: a trend line showing your fitness improving.