Target Heart Rate Calculator

What a training zone actually is

A heart-rate zone is a percentage, and a percentage needs something to be a percentage of. Every boundary on this page descends from one estimated number — the age-predicted maximum heart rate, standing in for the figure a supervised maximal exercise test would establish — and one rule for turning that number into beats per minute. Both parts are conventions. The arithmetic that applies them is exact in a way the number underneath them is not, which is the single most useful thing to know about any zone.

This calculator applies two of those rules. Enter an age alone and it takes plain percentages of the estimated maximum. Add a resting heart rate and it switches to the Karvonen heart-rate-reserve formula, which uses that second input and returns different beats per minute at the same nominal intensity. The companion guide — heart-rate zones explained — is the longer read: the same ground at more length, with 220 − age, the Karvonen algebra, and the zone 2 band each given the room they deserve.

220 − age, and how wide its spread is

The maximum used here comes from the conventional 220 − age rule. At age 30 it returns 190 bpm, and every figure below is that number multiplied by something. The rule is a population average with wide individual spread — being off by 10–15 bpm is common. A population average describes the centre of a distribution of measured maximums; it does not describe any particular person, and nothing in the formula guarantees that a given individual sits at that centre.

Two separate quantities are worth keeping apart here. One is what the formula does across ages: because the rule subtracts the age itself, the estimate falls beat-for-year, so at 30 it returns 190 bpm and at 45 it returns 175 bpm — 15 bpm apart across 15 years. The other is the spread quoted for the rule, 10–15 bpm, which applies at any single age and describes how far a measured maximum can sit from what the formula returns. The first is arithmetic and exact; the second is the reason the first should not be read to the beat.

The uncertainty also propagates unevenly, because a percent-of-max boundary is nothing more than intensity × maximum. Take those two maximums as a stand-in for a 15 bpm difference in the input, whatever its source: the 50% boundary moves from 95 to 88 bpm, while the 85% boundary moves from 162 to 149 bpm. The same difference in the input, scaled by the intensity applied to it — boundaries at the top of the ladder inherit more of it than boundaries at the bottom.

Two further limits travel with the convention, and both are taken up at the end of this page. It was characterized in adults rather than teenagers. And a measured maximum from a supervised test always beats the estimate — where one exists, the intensity percentages can be applied to that figure instead.

The Karvonen formula, written out

Karvonen's method, in full, is (maximum − resting) × intensity + resting. The bracket holds the heart-rate reserve: the span between the resting rate supplied as an input and the estimated maximum above it. The formula takes the intensity share of that span, then adds the resting rate back so the answer comes out as a heart rate rather than as a share of a range.

At the same nominal intensity it returns a higher number than a plain percentage does, and that is structural rather than incidental. Write i for the intensity fraction and expand:

(max − rest) × i + rest = i × max − i × rest + rest = i × max + rest × (1 − i)

The first term, i × max, is the percent-of-max figure. So Karvonen equals percent of maximum plus rest × (1 − i): the resting rate, scaled by however much intensity is left below 100%. That term is positive at every intensity this calculator prints, largest at the bottom of the ladder where (1 − i) is large, and it closes to nothing at 100%, where both conventions return the maximum itself.

Which is why "70% intensity" does not name a single heart rate. It names a convention, and two plans can both say 70% while meaning different beats per minute. The worked table below sets the two conventions side by side rather than averaging them, because the midpoint of two conventions is a number neither convention produced. The calculator itself never averages them either: it returns one ladder per set of inputs and names the method that produced it.

The 50–85% ladder, both ways

The calculator builds its ladder from 50% to 85% intensity, and prints it once, by one method: the left column below is what the form returns for an age entered alone, the right is what it returns for the same age once a resting heart rate is added. Setting them beside each other means asking the engine twice, which is what this page does at build time — the same function the form calls in your browser, run for age 30 with no resting rate and then again with a resting rate of 60 bpm.

Intensity	Percent of maximum	Karvonen, resting 60
50%	95 bpm	125 bpm
60%	114 bpm	138 bpm
70%	133 bpm	151 bpm
75%	143 bpm	158 bpm
80%	152 bpm	164 bpm
85%	162 bpm	171 bpm

Read across the 50% row and the two columns are 30 bpm apart; read across the 85% row and the gap is down to 9. That narrowing is the rest × (1 − i) term shrinking as i climbs, exactly as the algebra above requires — not a rounding artefact and not a disagreement to be split. The single worked figure quoted above the form, 70% intensity at 151 bpm, is the 70% row of this table.

What the resting-rate field does to the arithmetic

The resting heart rate is an input to a formula, not a reading this page interprets. Left empty, the calculator has a single number to work from and its boundaries move only with the age entered. Filled in, the reserve term appears, and the same age with a lower entry leaves a wider reserve while a higher entry leaves a narrower one.

Holding the age at 30 and changing nothing but that field, 70% intensity lands at 147 bpm for a resting entry of 48, at 151 bpm at 60, and at 155 bpm at 72. Two things move together there. Every band shifts upward as the entry rises, because the resting rate added back at the end is larger; and every band grows narrower, because the same 50–85% span is being applied to fewer beats of reserve. Both effects fall out of the formula rather than out of any judgement about the three entries.

The engine accepts ages from 10 to 100 and resting rates from 30 to 150 bpm, and it requires the resting entry to sit below the age-predicted maximum: a reserve of zero or less has no arithmetic meaning, so such an entry is refused with an explanation rather than answered with a number. Everything runs in your browser, and nothing you type into the form is transmitted or stored.

Zone 2, the 60–70% band

In the five-zone model, zone 2 is the 60–70% band — the easy-aerobic end of the same ladder, low enough that the rest × (1 − i) term is still large. At age 30, percent of maximum puts the band at 114–133 bpm; with a resting rate of 60, Karvonen puts the same nominal band at 138–151 bpm. The floor of the second sits above the ceiling of the first — they do not merely differ, they do not overlap at all.

The size of that separation follows the ladder above rather than being special to zone 2. At 60%, the band's floor, the two columns are 24 bpm apart; at 85% the gap is down to 9. The widest gap on the ladder is not inside zone 2 at all but below it, at the 50% rung, where the columns stand 30 bpm apart — the term is largest where (1 − i) is largest, and zone 2 sits near that end without occupying it.

The Zone 2 Calculator prints that band by percent of maximum from an age alone, and adds the Karvonen band beside it once a resting heart rate is entered. It is worth keeping the label separate from what it is often taken to stand for, though. The band above is a percentage range, which is why arithmetic can produce it at all; the same label is also used in senses that no formula applied to an age can produce. The two are not the same thing, and this page computes only the percentage band.

Where formula zones stop being useful

A zone number carries none of its own caveats on its face, so they are worth stating plainly.

• Heart-rate-affecting medication. Medications such as beta blockers make formula zones misleading. The numbers still compute; they no longer describe intensity the way they otherwise would. That is a question for a qualified healthcare professional rather than for a calculator.
• Teenagers. The 220 − age convention was characterized in adults rather than teenagers. The form accepts an age of 10 and up and will print a full ladder for any of them, but zones computed for a teenager are rough orientation at best.
• A measured maximum already exists. It always beats the estimate. Where a supervised test has produced one, the intensity percentages can be applied to that figure directly, and the 10–15 bpm spread described above simply goes away.
• Mixed conventions. A watch computing percent of maximum and a plan quoting Karvonen will disagree at the same nominal percentage by exactly the amount the algebra predicts. Which convention produced a number matters more than the number.

Every figure on this page was produced at build time by the same tested functions the form calls in the browser, from fixed inputs written into the page rather than from any live reading, so the prose and the code cannot drift apart — if they disagreed, the site would fail to build.

Frequently asked questions

Not medical advice: this calculator provides general educational estimates from published population formulas. It cannot account for your individual health context and must not be used to diagnose or treat any condition — consult a qualified healthcare professional before intensity-based training, particularly with a cardiac condition or heart-rate-affecting medication such as beta blockers. Data is processed locally in your browser and never transmitted. See the methodology page.