TL;DR
For a fast set of zones with nothing to sign up for, use the Calc Garden target heart rate calculator: enter your age, add a resting rate if you have one, and it shows your maximum heart rate and your fat-burn, cardio and peak zones the instant you type, with the formula on the page and no wearable needed. If you want a full five-zone model with a choice of maximum heart rate formulas, the Omni Calculator heart rate zone tool does more, and the McMillan calculator is best for running-specific zones. This is not an "only free one" claim: Omni, McMillan and calculator.net are all free too. The choice is really a quick three-zone answer versus a detailed five-zone model versus running paces.
What makes a heart rate zone calculator "best"
Every heart rate zone calculator runs the same core idea: estimate your maximum heart rate, then take percentages of it to mark the training zones. Because the arithmetic barely changes between tools, the right pick is decided by three things. The first is how many zones you actually want: a simple fat-burn, cardio and peak split, or a finer five-zone or six-zone grid built for structured plans. The second is how personal you want the numbers to be: a flat percentage of your maximum, or the Karvonen method that folds in your resting heart rate. The third is transparency: does the tool show the formula and let you sanity-check the beats-per-minute figures, or just hand back a coloured chart?
Those pull in slightly different directions, so there is no single winner for everyone. A simple three-zone calculator is unbeatable for a fast answer before a workout. A five-zone tool suits anyone following a plan written around specific zones, and a running-focused calculator is better if you want paces tied to each zone. The table below lines up four free options against exactly these points, so you can choose by what you need rather than by brand. Crucially, none of them needs a watch: the zones come from your age, so a calculator is enough.
The best free heart rate zone calculators compared
In the table a check means the tool does it cleanly, "Partial" means it does it with caveats, and a dash means it does not. The pricing row reflects each product as of 2026.
| Capability | Calc Garden | Omni | Calculator.net | McMillan |
|---|---|---|---|---|
| Price (as of 2026) | Free, no signup | Free, no signup | Free, no signup | Free, no signup |
| Works from age alone | Yes | Yes | Yes | Partial |
| No wearable or chest strap needed | Yes | Yes | Yes | Yes |
| Optional resting HR (Karvonen method) | Yes | Yes | Yes | Partial |
| Named training zones | 3 zones | 5 zones | 2 ranges | 6 zones |
| Choice of max HR formula (e.g. Tanaka) | No | Yes | Partial | Partial |
| Formula shown on the page | Yes | Partial | Partial | No |
| Zones tied to running paces | No | No | No | Yes |
| Runs entirely in your browser | Yes | Yes | Yes | Yes |
Read it honestly. Omni wins where you want detail: it splits effort into five zones and lets you switch the maximum heart rate formula, including the Tanaka estimate that many coaches now prefer over 220 minus age. McMillan wins for runners, because its six zones come with the training paces to match, which a plain heart rate tool cannot give. Calculator.net is a clean free all-rounder for a simple moderate-and-vigorous target range. Calc Garden wins on speed and clarity for the most common job: turn your age, and optionally a resting rate, into a maximum and three clear zones, with the formula on the page and the Karvonen method applied the moment you add a resting rate. It uses 220 minus age and three named zones rather than a menu of formulas, which is the honest trade-off for that simplicity.
Why you do not need a watch to find your zones
A common worry is that heart rate zones require a Garmin, Polar, Apple Watch or a chest strap. They do not. A wearable measures your heart rate live so you can see whether you are inside a zone during a session, which is genuinely useful for pacing effort in real time. But the zones themselves are fixed percentages of your estimated maximum heart rate, and that estimate comes from your age, not from any sensor. So a calculator can hand you the exact beats-per-minute boundaries with nothing on your wrist.
Calc Garden's target heart rate calculator runs client-side in your browser: enter your age and it shows your maximum heart rate and your fat-burn, cardio and peak zones straight away. Add your resting heart rate and it switches to the Karvonen reserve method for more personal numbers. If you want to take your pulse the old-fashioned way to check a session, count the beats in your neck or wrist for 15 seconds and multiply by four. The trade-off is honest and worth stating: a calculator gives you the target ranges, but only a monitor tells you your live heart rate mid-workout, so the two are complementary rather than rivals.
The formula, and a worked example
The starting point is your maximum heart rate, estimated as 220 minus your age. Each zone is then a band of percentages of that maximum: the fat-burn zone runs about 50 to 70 percent, the cardio zone 70 to 85 percent, and the peak zone 85 to 95 percent. Take a 40 year old. Their estimated maximum is 220 minus 40, or 180 beats per minute. The fat-burn zone is 50 to 70 percent of 180, which is 90 to 126 bpm. The cardio zone is 70 to 85 percent, or 126 to 153 bpm. The peak zone is 85 to 95 percent, or 153 to 171 bpm.
The Karvonen method personalises those bands using your resting heart rate. Subtract your resting rate from your maximum to get your heart rate reserve, multiply the reserve by the intensity, then add the resting rate back on. For the same 40 year old with a resting rate of 60, the reserve is 180 minus 60, or 120. A 70 percent target is 120 times 0.70 plus 60, which is 144 bpm, higher than the flat-percentage figure of 126. Calc Garden's target heart rate calculator lands pre-filled with a worked example and recomputes the moment you change your age or resting rate, so you can see how the zones shift rather than trust a hidden calculation. Remember that the maximum itself is an estimate that can sit 10 to 15 beats either side, so treat the numbers as a guide, not a hard limit.
Which one to use
Reach for Omni when you want a five-zone breakdown and a choice of maximum heart rate formulas, or McMillan when you are a runner who wants heart rate zones tied to training paces from a recent race time. Reach for calculator.net when you just want a simple moderate-and-vigorous target range on one page.
Reach for the Calc Garden target heart rate calculator when you want your maximum and three clear zones fast, with the Karvonen option, no signup and no wearable. From there, two related tools round out a training session's numbers: the running pace calculator turns a distance and time into pace per km and per mile, and the calories burned calculator estimates the energy a workout costs. For the wider set of explainers, the guides index collects the rest, including the best free running pace calculator and the best free calories burned calculator.