Heart Rate Zone Calculator
Build all five training zones under both methods at once, and see how far apart they are for the same person.
Heart Rate Zone Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Zone boundaries are conventions, not physiological thresholds.
- Every boundary inherits the ±7 bpm uncertainty of the estimated maximum.
- Heart rate at a given workload shifts with heat, altitude, illness, caffeine and sleep.
In short: At age 55 with a resting heart rate of 58, Zone 2 runs 102 to 119 bpm by percentage of maximum but 125 to 136 bpm by the Karvonen reserve method — a 23 bpm gap at the floor under the same zone label.
Formula
Both are called percentages, but only Karvonen is a percentage of the range you actually have available.
Worked Example
- Establish the anchors. Tanaka gives 169.5 bpm maximum at age 55; a resting rate of 58 gives 111.5 bpm of reserve.
- Apply the percentage method. 60% to 70% of 169.5 puts Zone 2 at 102 to 119 bpm, ignoring the resting rate entirely.
- Apply Karvonen. 58 + (111.5 × 60%) to 58 + (111.5 × 70%) puts Zone 2 at 125 to 136 bpm.
- Measure the disagreement. 23 bpm at the Zone 2 floor. The percentage floor is only 39.19% of actual reserve.
- Distribute the training. Roughly 80% of time in Zones 1 and 2, the rest in Zones 4 and 5, with little in Zone 3.
Two methods, one person, and a 23 bpm disagreement about where Zone 2 starts. The percentage-of-maximum method is the one built into most watches and most training articles, and it systematically prescribes easier work than intended because it ignores that your heart never actually goes below its resting rate. Its Zone 2 floor here sits at 39.19% of your real reserve rather than 60% of anything. What makes this more than a technicality is who it affects: the gap grows with resting heart rate, so a deconditioned person with a resting rate of 85 gets an error of 34 bpm while a trained athlete at 45 gets 18. The people most dependent on the prescription being right receive the worst version of it.
Strengths & Limits Of This Model
Where this engine is strong
- Computes both methods so the disagreement is explicit rather than hidden.
- Shows what the percentage method's zone floor really is as a fraction of reserve.
- Identifies that the error is largest for the least conditioned users.
Where it stops
- Cannot replace lactate or ventilatory threshold testing.
- Assumes a single resting and maximum value rather than daily variation.
Practical Use Cases
Setting up zones on a watch or platform
Most default to percentage of maximum. If the platform allows a Karvonen or reserve option, use it and enter your resting rate.
Understanding why easy runs feel too easy
Percentage-based Zone 2 often falls below genuine aerobic effort. The Karvonen floor is usually closer to what training at that zone should feel like.
Building a polarised training week
Roughly 80% easy, the rest hard, little in between. Check your aerobic capacity with the VO2 Max Calculator.
Prescribing one specific session
For a single target intensity rather than the full table, use the Target Heart Rate Calculator.
Methodology & Editorial Standards
Training zones divide the range between rest and maximum effort into bands that correspond loosely to distinct physiological adaptations, and the engine computes all five under both methods in common use so the difference between them is visible rather than assumed. The percentage method takes simple fractions of maximum heart rate and is the approach built into most consumer devices; it ignores resting heart rate entirely, which means it implicitly treats zero beats per minute as the bottom of the training range and therefore places every zone boundary lower than intended. The Karvonen method works within heart rate reserve, the span from resting rate to maximum, adding a percentage of that reserve to the resting rate, which is the physiologically coherent construction because the heart cannot work below its resting rate. The engine quantifies the disagreement at the Zone 2 floor and reports what the percentage method's floor actually represents as a fraction of reserve, which is consistently far below the nominal figure. Critically, the discrepancy scales with resting heart rate, so the error is largest for the least conditioned users. Zone boundaries are presented as bands rather than thresholds, since they inherit the roughly seven beat uncertainty in any estimated maximum and since heat, altitude, illness and sleep all shift heart rate at a fixed workload. This calculator is an educational estimate and is not medical advice, diagnosis or treatment. Heart rate formulas are population averages with wide individual variation, and they do not account for medication, cardiac conditions, altitude, heat or illness. Beta blockers and other rate-limiting drugs make every age-based estimate on this page invalid. Anyone with a cardiac history, anyone taking heart rate medication, and anyone who is currently sedentary should obtain medical clearance before beginning vigorous exercise or attempting any maximal effort. Stop exercising and seek medical attention for chest pain, undue breathlessness, dizziness, fainting or an irregular heartbeat. The engine implements the standard published formula for this calculation. Inputs are validated for domain and sign before evaluation, and any undefined case returns an em-dash rather than a spurious value.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Heart Rate Zone Calculator — 20 Expert FAQs
20 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
What are the five heart rate zones?
Recovery, aerobic base, tempo, threshold and maximal — conventionally 50–60, 60–70, 70–80, 80–90 and 90–100 percent.
What is the Karvonen formula?
Resting HR + (reserve × zone percentage). It works within the range you actually have rather than from zero.
Which method is more accurate?
Karvonen, because it accounts for resting heart rate. Percentage of maximum systematically prescribes easier training.
How different are they?
23 bpm at the Zone 2 floor here — 102 versus 125 bpm for the same person under the same label.
Why does the gap grow with resting heart rate?
Because percentage of maximum ignores the resting rate. The higher it is, the more of your actual range the method mis-states.
What heart rate is Zone 2 for me?
125 to 136 bpm by Karvonen at age 55 with a resting rate of 58. By percentage of maximum it would read 102 to 119.
How much training should be in Zone 2?
Most of it. Around 80% of endurance training time belongs in Zones 1 and 2, with the remainder hard.
What is wrong with Zone 3?
Nothing inherently, but it accumulates fatigue without driving peak adaptation. Most people spend too much time there by default.
Should I use measured or estimated maximum?
Measured, always, if you have one from a genuine maximal effort with a chest strap. It removes the largest source of error.
Do zones shift day to day?
The boundaries do not, but your heart rate at a given effort does. Heat, altitude, illness, caffeine and poor sleep all move it.
Is the talk test reliable?
Surprisingly so. Full sentences means Zone 2; short phrases means Zone 3 to 4; single words means Zone 5. Use it to sanity-check the numbers.
Why does my watch disagree with this?
Most watches use percentage of maximum with a 220 − age default — two separate sources of error compounding.
Are zone boundaries physiologically real?
Not as sharp lines. They are convenient divisions of a continuum, and they inherit the ±7 bpm uncertainty of your estimated maximum.
Does zone training work for beginners?
Yes, and the discipline of staying easy is the main benefit. Beginners routinely train their easy sessions too hard.
What about lactate threshold testing?
A laboratory or field lactate test defines your zones far more precisely than any age-based formula, and it is the honest upgrade.
Do beta blockers change my zones?
Completely. They suppress heart rate at every intensity, so zones must be set by perceived exertion or clinically rather than by formula.
Is this heart rate zone calculator free to use?
Yes. It is free, requires no account, and has no usage limits. ApexConverter is funded by contextual advertising, never by selling user data.
Is my data sent to a server?
No. The engine runs as Vanilla JavaScript inside your browser under our Zero-Server Client-Side Execution model. Your figures are computed locally and are never transmitted, logged, or stored.
How accurate is this calculator?
It applies the standard closed-form formula in IEEE-754 double precision, rounding only at the display layer. The engine is reconciled against an independent reference implementation before release.
Does it work on mobile?
Yes. The interface is mobile-first with numeric keypad hints and is tested down to a 320-pixel viewport with no horizontal scrolling.