Karvonen Formula Calculator
Get a personalized target heart rate band with the Karvonen (heart rate reserve) method. Enter your age, resting heart rate, and an intensity range in percent — or type in a measured max heart rate if you know it.
Example: with Age (years) 40 · Resting heart rate (bpm) 65 · Intensity, low end (%) 60 · Intensity, high end (%) 80 → Target heart rate: 134 to 157 bpm (60% to 80% of reserve).
- Heart rate reserve (HRR)115 bpm (max 180 minus resting 65)
- Max heart rate used180 bpm — 220 minus age convention
Computed by the calculator below using its default values. Change any input to see your own numbers.
Karvonen THR = ((HRmax − HRrest) × %intensity) + HRrest. Anchoring to your resting rate is what makes it personal — two 40-year-olds with resting rates of 50 and 75 get different zones.
Why Karvonen beats plain percent-of-max
The common shortcut — take 220 minus your age, multiply by 70% — ignores the floor your heart never goes below. The Karvonen method works with heart rate reserve: the span between resting and maximum. An intensity percent is applied to that usable span, then your resting rate is added back. The result tracks exercise effort (%VO2 reserve) much more closely, which is why ACSM's exercise-prescription guidelines are written in %HRR terms.
Fitness shows up in the inputs. As training lowers your resting heart rate, your reserve widens and every zone shifts — recompute after a few months. The 220 − age ceiling is only a population convention with a spread of roughly ±10 bpm; a measured max from a field test or a hard race finish is better, and the calculator accepts one.
How it’s calculated
THR = ((HRmax − HRrest) × %intensity) + HRrest (Karvonen). HRmax = 220 − age by convention unless you enter a measured max. Heart rate reserve (HRR) = HRmax − HRrest. Example at age 40, resting 65: HRmax 180, HRR 115, so 60% to 80% gives 134 to 157 bpm. Intensity bands follow ACSM: moderate 40-59% HRR, vigorous 60-89% HRR.
Estimates only, not medical advice — 220 − age misses real maxes by ±10 bpm or more, and beta-blockers, stimulants, and heart conditions change everything; clear new intense exercise with your doctor if you have cardiac risk factors.
ACSM intensity bands in %HRR (example: age 40, resting 65)
| Intensity | % of reserve | Target bpm | Feels like |
|---|---|---|---|
| Light | 30 - 39% | 100 - 110 | Easy movement, full sentences |
| Moderate | 40 - 59% | 111 - 133 | Brisk walk; talking takes effort |
| Vigorous | 60 - 89% | 134 - 167 | Running, hard cardio; short phrases |
| Near-maximal | 90%+ | 169 and up | Intervals, race finishes |
Bands: ACSM exercise-intensity classification by %HRR. Example bpm computed with Karvonen at HRmax 180, resting 65; rounded.
Common mistakes
- Applying the percent to max heart rate instead of the reserve — at 70% that understates a typical target by 10-20 bpm.
- Measuring resting heart rate after coffee, mid-day, or standing — take it lying down, just after waking, averaged over a few days.
- Treating 220 − age as your true max; it is a convention with a wide spread, so use a measured max when you have one.
- Ignoring medications: beta-blockers cap heart rate, which makes every HR-based zone misleading.
Frequently asked questions
What is the Karvonen formula?
Target HR = ((HRmax − HRrest) × %intensity) + HRrest. With HRmax estimated as 220 − age: a 40-year-old with resting 65 gets ((180 − 65) × 0.70) + 65 = 145.5, so about 146 bpm at 70% intensity.
How is this different from 70% of max heart rate?
Percent-of-max multiplies the ceiling only; Karvonen scales the span between resting and max, then adds resting back. For the 40-year-old above, 70% of max is 126 bpm — a full 20 bpm easier than the Karvonen 146. The two scales are not interchangeable.
What intensity should I train at?
ACSM calls 40-59% of heart rate reserve moderate and 60-89% vigorous. Most steady cardio lives at 50-75% HRR; keep easy days near the bottom and save 85%+ for short intervals.
How do I find my resting heart rate?
Before getting out of bed, count your pulse for 60 seconds (or let a tracker read it overnight), and average 3-5 mornings. Illness, alcohol, and poor sleep push it up temporarily.
Is 220 minus age accurate?
It is a rough population convention — individual maxes scatter around it by ±10-12 bpm, and it tends to underestimate for older adults. If you have a measured max from a stress test or all-out effort, enter it; and if you have any heart condition, get zones from your cardiologist rather than a formula.