Target heart rate for exercise is calculated with the Karvonen formula as (HRmax − resting HR) × intensity% + resting HR, where HRmax is estimated as 220 − age. That single equation turns a percentage of effort into a specific beats-per-minute number you can chase on a watch or chest strap during a workout. The reason fitness coaches prefer Karvonen over the older "percentage of max heart rate" approach is that it folds your resting pulse back into the answer, so the result reflects how fit you already are. A trained runner and a sedentary office worker of the same age can both be told to train at 70%, and the formula will hand them two different bpm targets that suit their actual condition instead of one shared number that suits neither. The whole calculation runs on three inputs you provide — your age, a resting pulse measured first thing in the morning, and a chosen intensity — which is why a dedicated Target Heart Rate Calculator built on this formula returns the answer instantly without any spreadsheets or manual arithmetic.
The Karvonen Formula and Why It Replaces Simple Percentages
The Karvonen formula, also called the heart-rate reserve (HRR) method, has three parts you can read in plain English. The first part, HRmax, is your maximum heart rate — the highest your heart can sustainably beat — estimated by the Fox equation as 220 minus your age. The second part, resting HR, is your pulse when you are calm and still, and it is added back in at the end so the targets sit above your baseline rather than starting from zero. The third part is intensity%, the share of your heart-rate reserve you want to spend, expressed as a decimal. Together they produce a target bpm that is sensitive to your age and your current fitness, instead of just your age.
To make the formula concrete, take a 30-year-old with a resting heart rate of 60 bpm. HRmax is 220 − 30 = 190, and the heart-rate reserve is 190 − 60 = 130. At 70% intensity the calculation reads (130 × 0.70) + 60 = 91 + 60 = 151, so the target is 151 bpm. Drop the intensity to 60% and the target slides down to 138 bpm; raise it to 80% and the target climbs to 164 bpm. Those are the numbers a Target Heart Rate Calculator returns in one click, and the same three inputs at any other age produce a proportional shift.
Three Numbers You Need Before You Start
Before you open the calculator, collect the three inputs the formula needs. The first is your age in whole years — the Fox equation is simple enough that rounding to the nearest birthday is fine. The second is your resting heart rate, which the method treats as a fixed personal constant rather than something you re-measure every session. The third is your target intensity as a percentage, chosen from the training zone you want to spend most of your session in.
Measuring resting heart rate correctly is the step most readers skip and the step that matters most. Take your pulse for a full 60 seconds rather than counting for 15 and multiplying, because the multiplication amplifies small timing errors. Do it first thing in the morning, before getting out of bed, before caffeine, and ideally on three to five different days. Average the readings — caffeine, stress, illness, dehydration, and poor sleep all push the number upward, so a single bad morning can quietly inflate every target the calculator hands you for the rest of the year.
Choosing intensity is more about training goal than math. Roughly 50–70% of your heart-rate reserve is moderate aerobic work — brisk walking, easy cycling, steady rowing — and about 70–85% is vigorous, covering running, tempo efforts, and intervals. Beginners usually start near the bottom of that range and let the same effort feel easier over weeks as their resting pulse gradually drops.
Run the Three-Step Calculation
- Enter your age in years in the first field. The tool uses it to estimate HRmax as 220 − age, so a 30-year-old gets an HRmax of 190 and a 50-year-old gets an HRmax of 170.
- Enter your resting heart rate in bpm, ideally the morning average you measured over several days. A trained adult often sits in the 50s while a less active adult may sit in the 70s, and that difference is exactly what the formula uses to personalize the result.
- Enter your target intensity as a percentage — for example 70 for a steady aerobic session — and read the target bpm plus the broader 50%–85% training zone that the calculator displays for the same inputs.
Reading Your 50% to 85% Training Zone
The single bpm at your chosen intensity is your anchor, but the calculator also shows a wider zone spanning 50% to 85% of your heart-rate reserve so you can see the full aerobic-to-vigorous range in one view. Most cardio, fat-burning, and endurance work fits inside this window, and it is the range beginners should live in for the first several weeks of training. The exact bpm at the bottom and top of that band depends on your age and resting heart rate, so use the calculator rather than memorizing the numbers.
| Intensity (% of HRR) | Zone | How it usually feels | Typical activities |
|---|---|---|---|
| 50–60% | Recovery / easy base | Breathing easy, can sing | Warm-ups, walking, active recovery days |
| 60–70% | Fat-burning / light aerobic | Brisk and slightly sweaty, full conversation possible | Brisk walking, easy cycling, steady rowing |
| 70–80% | Aerobic / cardio | Hard breathing, only short phrases possible | Jogging, tempo runs, longer cycling efforts |
| 80–85% | Vigorous / threshold | All-out sustainable only in short bursts, speaking nearly impossible | Intervals, hill repeats, race-pace work |
Below about 50% you are basically building a base and recovering, and pushing above 85% edges toward anaerobic effort that is hard to sustain for more than a few minutes. The Karvonen formula will happily return numbers outside that window, but doing so usually signals a goal mismatch — for example, picking 90% intensity for a "fat-burn" session — rather than a smart training choice.
Cross-Checking Effort Without a Heart-Rate Monitor
Numbers are useful, but days happen — illness, heat, poor sleep, dehydration, and stress all shift your real response away from the average. Two field checks sit alongside the calculated target so you can sanity-check what the watch is telling you.
The talk test is the simplest. At moderate intensity you can hold a conversation in full sentences; at vigorous intensity you can only manage short phrases between breaths; above 85% you cannot really speak at all. If your watch says 70% but you are gasping for single words, you are probably working harder than the formula assumes for that day.
Rating of perceived exertion, or RPE, is a 1-to-10 scale of how hard a session feels subjectively. A rough pairing is RPE 3 to 4 for moderate work, RPE 5 to 7 for vigorous work, and RPE 8 and above for near-maximal intervals. Used alongside the calculated zone, RPE catches the days when your calculated target is technically right but your body is responding differently, and it gives you a backup on the days you forget to strap on a monitor.
Limits of 220 Minus Age and When to See a Doctor
The Fox equation is a population average, not an individual measurement. It can be off by roughly 10–12 bpm in either direction for any given person, which is enough to push a moderate-zone session into a vigorous one without warning. Treat the calculator's output as a starting estimate, and if you need an exact HRmax — for example, to set precise threshold paces — a supervised exercise test is the only way to get one. For a deeper look at how maximum heart rate is defined and measured, the Wikipedia heart rate article walks through the common formulas and their population-level accuracy.
The target heart rate tool is a general fitness aid, not medical advice. If you have a diagnosed heart condition, take medication that affects heart rate such as beta blockers, are pregnant, are returning to exercise after illness or surgery, or are brand new to structured training, talk to a doctor before using these numbers. Beta blockers in particular lower both resting and maximum heart rate, so the formula will underestimate the effort and the targets will feel harder than the bpm suggests.
All of this is calculated locally in your browser, so the age, resting pulse, and intensity you enter never leave your device. That makes it easy to experiment with different intensities, re-run the calculation after you take a fresh morning resting reading, or share the output with a coach without worrying about a server somewhere logging your numbers.