What is the Karvonen formula?

Published by Finnish physiologist Martti Karvonen in 1957, it calculates target heart rate as: resting HR + (heart rate reserve × intensity%), where heart rate reserve = max HR − resting HR. It's considered more personalized than simply using a flat percentage of max heart rate, because it accounts for your fitness level via resting HR.

How is max heart rate estimated if I don't know mine?

This tool defaults to the widely used 220 − age formula, a population-average estimate with a fairly wide error margin (±10–12 bpm) for any individual. If you've had a supervised max-HR field or lab test, enter that exact number instead for more accurate zones.

Why does a lower resting heart rate widen my zones?

Heart rate reserve is max HR minus resting HR — a fitter person with a lower resting heart rate has a larger reserve, which spreads every zone's bpm range wider apart. This is one reason Karvonen zones are considered more personalized than simple max-HR percentages.

Is Zone 2 the same as the 'fat-burning zone'?

Zone 2 (60–70% of heart rate reserve) is often called the aerobic-base zone in training literature. Avoid over-interpreting any zone as a guaranteed fat-loss switch — total calories burned and overall diet matter far more for body composition than which zone a given workout falls into.

Heart Rate Zone Calculator

Calculate five heart-rate training zones from age and resting heart rate using the Karvonen formula, with an optional lab-tested max HR override.

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Formula: Karvonen: target HR = resting HR + (max HR − resting HR) × intensity%; max HR default = 220 − age

Worked examples

30-year-old, resting HR 60, no lab-tested max
The common case: no lab-tested max heart rate, so the calculator falls back to the 220-minus-age estimate.
45-year-old with a lab-tested max HR of 180
Someone who has done a supervised max-HR test can override the age-based estimate for more accurate zones.
25-year-old, resting HR 55 (well-trained athlete)
A low resting heart rate from aerobic training widens the heart rate reserve, shifting every zone's bpm range.

What this calculator does

Training "zones" divide your heart rate range into bands tied to different training effects — easy aerobic work, moderate effort, and hard, near-maximal efforts. This tool calculates five zones personalized to your age (or a lab-tested max heart rate) and your resting heart rate, using a method that accounts for your individual fitness level rather than a single flat percentage of max heart rate.

The Karvonen method

Finnish physiologist Martti Karvonen published this approach in 1957. Instead of calculating a zone as a flat percentage of maximum heart rate, it first works out your heart rate reserve — the gap between your maximum heart rate and your resting heart rate — and calculates each zone as a percentage of that reserve, added back to your resting rate: target HR = resting HR + (heart rate reserve × intensity%). This matters because two people with the same max heart rate but very different resting heart rates (a sign of different fitness levels) end up with meaningfully different training zones under Karvonen, which flat max-HR percentages don't capture.

Estimating max heart rate

If you haven't had a supervised max-HR test, this tool defaults to the widely used 220 − age formula. It's a population average with a real margin of error — some individuals run 10–15 bpm above or below what the formula predicts, purely due to natural variation. If you've done a maximal-effort field test (a hard interval session or a supervised fitness assessment) and know your actual max heart rate, entering it directly will give you noticeably more accurate zones than the age-based estimate.

The five zones

The zones run from very light (50–60% of heart rate reserve, for warm-up and recovery) through light, moderate and hard, up to maximum (90–100%, for short, high-intensity efforts). Different coaching systems bound these zones slightly differently — this tool uses the common five-zone split found across most Karvonen-based plans. Zone 2, often called the aerobic-base zone, gets particular attention because sustained work there builds aerobic capacity with comparatively low fatigue cost.

Using the zones

Zones are a training tool, not a hard boundary — use them to guide pacing (an "easy run" sits in zone 1–2; hard intervals target zone 4–5) rather than obsessing over exact bpm minute to minute. Heart rate also drifts upward over a long effort at constant pace (cardiac drift), and runs higher in heat or with poor sleep, so treat any single reading in context.

Limits

This tool doesn't diagnose any cardiac condition and isn't a substitute for a supervised stress test if you have reason to be concerned about your heart's response to exercise. The age-based max-HR estimate is a population average, not a personal measurement, and beta-blockers, certain medical conditions and individual physiology can shift the true numbers meaningfully. This is a training-planning estimate, not medical advice — talk to a qualified professional before starting an intense exercise program if you have any underlying health concerns.

Frequently asked questions

What is the Karvonen formula?: Published by Finnish physiologist Martti Karvonen in 1957, it calculates target heart rate as: resting HR + (heart rate reserve × intensity%), where heart rate reserve = max HR − resting HR. It's considered more personalized than simply using a flat percentage of max heart rate, because it accounts for your fitness level via resting HR.
How is max heart rate estimated if I don't know mine?: This tool defaults to the widely used 220 − age formula, a population-average estimate with a fairly wide error margin (±10–12 bpm) for any individual. If you've had a supervised max-HR field or lab test, enter that exact number instead for more accurate zones.
Why does a lower resting heart rate widen my zones?: Heart rate reserve is max HR minus resting HR — a fitter person with a lower resting heart rate has a larger reserve, which spreads every zone's bpm range wider apart. This is one reason Karvonen zones are considered more personalized than simple max-HR percentages.
Is Zone 2 the same as the 'fat-burning zone'?: Zone 2 (60–70% of heart rate reserve) is often called the aerobic-base zone in training literature. Avoid over-interpreting any zone as a guaranteed fat-loss switch — total calories burned and overall diet matter far more for body composition than which zone a given workout falls into.

These calculators give general estimates from published formulas. They are not medical advice and do not account for your individual health; talk to a qualified professional before changing your diet or training.