“Just keep your heart rate between 50% and 85% of your max” is the standard advice on almost every gym wall and fitness app — and it quietly assumes two things that usually aren’t true: that everyone’s maximum heart rate follows the same formula, and that everyone starts counting from zero. Neither is accurate. A 45-year-old marathon runner and a 45-year-old who hasn’t exercised in years can have the same age-predicted maximum heart rate and still need completely different target zones, because their resting heart rates — and therefore their actual heart rate reserve — are nothing alike.
This guide walks through both ways to calculate your target heart rate zones: the simple percentage-of-max method most calculators default to, and the Karvonen formula, which factors in your resting heart rate for a more personalized number. You’ll get the exact formulas, a five-zone reference table, and three fully worked examples showing exactly when the two methods agree — and when they don’t.
What Is a Target Heart Rate Zone?
Your target heart rate zone is the range of beats per minute (bpm) you should aim for during exercise to get a specific training effect — whether that’s gentle fat-burning activity, steady aerobic conditioning, or maximum-effort interval work. The American Heart Association defines two broad bands: moderate-intensity activity at roughly 50–70% of your maximum heart rate, and vigorous activity at roughly 70–85%.
Those percentages are useful as a starting point, but they only tell half the story. Two people with the same maximum heart rate can be at very different points in their actual cardiovascular effort at the same bpm, because the percentage doesn’t account for how low your heart rate sits at rest. That’s the gap the Karvonen formula was built to close — more on that below.
Step 1: Estimate Your Maximum Heart Rate
Both calculation methods start from the same number: your maximum heart rate (MHR), the highest bpm your heart can reasonably sustain during exertion. Unless you’ve had it measured directly in a lab or supervised stress test, it’s estimated from your age using one of two formulas.
| Formula | Equation | Notes |
|---|---|---|
| Fox formula (classic) | MHR = 220 − age | In use since 1971; the formula most calculators default to. |
| Tanaka formula | MHR = 208 − (0.7 × age) | From a 2001 meta-analysis of over 18,000 subjects; commonly cited as a closer estimate across a wider age range. |
The two formulas aren’t far apart, but they diverge in opposite directions depending on your age. They produce an identical result at age 40. Below 40, the Fox formula gives a slightly higher MHR than Tanaka’s; above 40, it gives a slightly lower one — and the gap widens the further your age sits from 40. At 20, Fox puts MHR at 200 versus Tanaka’s 194. At 60, Fox gives 160 versus Tanaka’s 166. Neither formula is exact for any one individual — both carry a published margin of error of roughly ±10–12 bpm — so treat the result as a planning estimate, not a lab measurement.
Step 2: Choose Your Zone Calculation Method
Once you have an MHR, there are two different ways to turn it into a target zone.
The simple %MHR method
This is the version used by most quick calculators:
Target HR = MHR × intensity%
It’s fast and needs only your age, but it treats everyone’s heart rate as starting from zero — which no one’s actually does.
The Karvonen formula (heart rate reserve method)
The Karvonen formula adds your resting heart rate (RHR) into the calculation, using what’s called your heart rate reserve — the gap between how low your heart rate sits at rest and how high it can go at maximum effort:
Heart Rate Reserve (HRR) = MHR − RHR
Target HR = (HRR × intensity%) + RHR
Because it’s anchored to your own resting rate instead of zero, Karvonen produces a more individualized zone — and, as the worked examples below show, the two methods can disagree by 10–40 bpm depending on how far your resting heart rate sits from average.
The 5 Heart Rate Training Zones
Most heart rate monitors and fitness apps break the 50–100% range into five named zones, each tied to a different training purpose:
| Zone | % of MHR (or HRR) | Purpose |
|---|---|---|
| Zone 1 — Warm Up | 50–60% | Easy recovery pace, warm-up and cool-down |
| Zone 2 — Fat Burn | 60–70% | Light, sustainable cardio; higher proportion of calories from fat, but fewer total calories burned per minute |
| Zone 3 — Aerobic | 70–80% | Builds cardiovascular endurance; the “steady-state cardio” zone |
| Zone 4 — Anaerobic | 80–90% | Hard effort, improves speed and lactate threshold |
| Zone 5 — VO2 Max | 90–100% | Maximum effort, short intervals only |
A quick note on the “fat burn” zone, since it’s widely misunderstood: Zone 2 does burn a higher percentage of calories from fat, but Zone 3 and Zone 4 burn more total calories — and more total fat — in the same amount of time, simply because you’re working harder. The name describes the fuel mix, not which zone is “best” for fat loss.
How to Measure Your Resting Heart Rate
The Karvonen formula is only as accurate as your resting heart rate input, so it’s worth measuring it properly rather than guessing:
- Measure first thing in the morning, before you get out of bed or have coffee.
- Place two fingers on your wrist (radial artery) or neck (carotid artery) — not your thumb, which has its own pulse.
- Count beats for a full 60 seconds, or count for 30 seconds and multiply by two for a quicker but slightly less precise reading.
- Repeat over 3–4 mornings and average the results — resting heart rate can swing 3–5 bpm night to night with sleep quality, hydration, and stress.
A typical adult resting heart rate falls between 60–100 bpm; well-trained endurance athletes often sit in the 40s–50s.
Worked Example 1: Full Zone Breakdown for an Average Adult
Profile: Age 30, resting heart rate 70 bpm (close to the population average).
MHR (Fox formula) = 220 − 30 = 190 bpm
Heart Rate Reserve = 190 − 70 = 120 bpm
| Zone | Karvonen range (bpm) |
|---|---|
| Zone 1 — Warm Up (50–60%) | 130–142 |
| Zone 2 — Fat Burn (60–70%) | 142–154 |
| Zone 3 — Aerobic (70–80%) | 154–166 |
| Zone 4 — Anaerobic (80–90%) | 166–178 |
| Zone 5 — VO2 Max (90–100%) | 178–190 |
With a resting heart rate close to average, these Karvonen zones land fairly close to what the simple %MHR method would give (for comparison, the simple method’s Zone 3 here would be 133–152 bpm versus Karvonen’s 154–166) — the gap is real but modest. That gap grows a lot wider at either end of the fitness spectrum, as the next two examples show.
Worked Example 2: A Trained Athlete With a Low Resting Heart Rate
Profile: Age 45, competitive cyclist, resting heart rate 50 bpm.
MHR (Fox formula) = 220 − 45 = 175 bpm (Tanaka formula gives 177 bpm — close enough here not to matter much).
Heart Rate Reserve = 175 − 50 = 125 bpm
Targeting Zone 3 (Aerobic, 70–80%) with the simple %MHR method: 175 × 0.70 to 175 × 0.80 = 123–140 bpm.
Targeting the same zone with the Karvonen formula: (125 × 0.70) + 50 to (125 × 0.80) + 50 = 138–150 bpm.
That’s a 15 bpm gap at the low end. For a cyclist this fit, training at the simple method’s 123 bpm would barely register as real aerobic effort — their Karvonen-calculated floor of 138 bpm is a much closer match to genuine aerobic intensity for their fitness level.
Worked Example 3: A Beginner With a High Resting Heart Rate
Profile: Age 52, new to structured exercise, resting heart rate 82 bpm.
MHR (Fox formula) = 220 − 52 = 168 bpm
Heart Rate Reserve = 168 − 82 = 86 bpm
Targeting a moderate-intensity walking program (50–70%) with the simple %MHR method: 168 × 0.50 to 168 × 0.70 = 84–118 bpm.
Targeting the same intensity with the Karvonen formula: (86 × 0.50) + 82 to (86 × 0.70) + 82 = 125–142 bpm.
Here the gap is much larger — 41 bpm at the low end. The simple method’s 84 bpm target sits barely above this person’s own resting rate of 82, which in practice means almost no real exertion. The Karvonen target of 125 bpm is a far more honest floor for what “moderate effort” should actually feel like for someone starting from this fitness level. The rule of thumb: the further your resting heart rate sits from roughly 70 bpm in either direction, the more the two methods disagree, and the more it’s worth doing the Karvonen calculation properly.
Common Mistakes When Using Heart Rate Zones
- Using a stale resting heart rate. RHR changes with fitness level, sleep, illness, and heat — a number from a year ago can be meaningfully off.
- Treating 220 − age as exact. It’s a population average with a real error margin; a measured max heart rate from a supervised test will always be more accurate than any formula.
- Chasing the “fat burn” zone exclusively. As covered above, it burns a higher percentage of fat calories but fewer total calories than harder zones — it’s one useful tool, not the only one.
- Ignoring medication effects. Beta-blockers and some other heart or blood pressure medications blunt heart rate response to exercise, which can make percentage-based zones unreliable; perceived exertion matters more in that case.
- Not re-checking zones as fitness changes. Resting heart rate typically drops as cardiovascular fitness improves, which shifts your Karvonen zones upward over time — recalculate every few months rather than using one number indefinitely.
Frequently Asked Questions
Which method should I actually use — simple %MHR or Karvonen?
Karvonen is more accurate for most people because it accounts for your individual resting heart rate rather than assuming everyone starts from zero. The simple %MHR method is fine as a rough starting point if you don’t know your resting heart rate yet, but as the worked examples above show, the difference can be large enough to matter — especially if your fitness level is well above or below average.
Is the 220 − age formula actually accurate?
It’s a reasonable population-level estimate, not an individual measurement. Published research puts its margin of error at roughly ±10–12 bpm for any given person, and the Tanaka formula (208 − 0.7 × age) is often cited as a closer estimate, particularly past age 40. If precision matters — for example, for structured athletic training — a supervised max heart rate test is the only way to get an exact number.
What heart rate zone is best for burning fat?
Zone 2 (60–70% of MHR) burns a higher percentage of calories from fat, but Zone 3 and Zone 4 burn more total calories — and often more total fat grams — per minute because the effort is higher. For overall fat loss, total calories burned across a week usually matters more than which single zone you trained in.
Can I use target heart rate zones if I’m pregnant or have a heart condition?
Talk to your doctor before using age-predicted heart rate zones if you’re pregnant, have a diagnosed heart condition, or take medication that affects heart rate (like a beta-blocker). These formulas are built for the general healthy population and may not apply to your situation.
How do I check my heart rate during a workout without a monitor?
Stop briefly, place two fingers on your wrist or neck, and count your pulse for 15 seconds, then multiply by four. It’s less precise than a chest strap or wrist-based heart rate monitor, which read continuously, but it’s a reasonable manual check mid-workout.
Why does my fitness watch give a different max heart rate than the formula?
Wearables often use their own proprietary estimation models, sometimes refined by your actual recorded heart rate data over time, rather than a single age-based formula. That can make them more personalized than a flat calculation — but like any estimate, they’re still not a substitute for a lab-measured max heart rate.
Once you know your target zones, you can pair them with CheckMatter’s BMR & Calorie Calculator to estimate how many calories a session in a given zone is likely to burn, or use the Macro Calculator to match your nutrition to your training load.