How to get accurate heart rate from a watch

Most of this is free and takes a minute. The steps come from Garmin's and Polar's own manuals, so they're manufacturer guidance and not test results. No study I read measures how much each step helps on a given watch.

I don't test devices and I haven't worn any watch named here. Checked as of 3 November 2026.

A tracker isn't a medical device. Wearable readings are estimates for general fitness and wellness, and they don't diagnose or treat any condition. If you have symptoms or concerns, talk to a clinician. If you have a heart condition, follow your care team's guidance on training zones rather than a watch reading. Etiwy and colleagues (peer-reviewed, 2019) found optical monitors less accurate than an electrode strap in 80 cardiac rehab patients.

Step 1: move it up your arm

Polar's Vantage V3 manual says to wear the watch on top of your wrist, "at least a finger's width up from the wrist bone". For training it goes further: slide it higher and wear the band a bit tighter. Garmin's Forerunner 265 manual agrees on the placement, above the wrist bone.

Step 2: get the tension right

Garmin says "snug but comfortable". Polar gives you an actual check, and it's a good one. Push the band lightly up from both sides of your arm. If the sensor lifts off the skin, or you can see the LED shining, it's too loose.

After the session, loosen it. Polar says so, and your skin will agree.

Step 3: clean skin, clean sensor

From the Garmin manual:

• Clean and dry your arm before you put the watch on.
• Avoid sunscreen, lotion and insect repellent under it.
• Rinse the watch with fresh water after each workout.
• Avoid scratching the sensor on the back.

Polar suggests a mild soap and water after sweaty sessions, then letting the watch dry before charging.

Step 4: warm up before you trust it

Both makers say this. Garmin suggests 5 to 10 minutes and a heart rate reading before the activity starts, warming up indoors if it's cold, and waiting until the heart-rate icon is solid. Polar suggests wearing the watch for a few minutes first, and warming the skin if your hands get cold easily.

Cold hands, then, are a fair first suspect on a winter morning.

Step 5: know its limits

Fit won't rescue everything. Zhang and colleagues (2020, peer-reviewed meta-analysis, 44 articles and 15 brands; abstract read, funding unchecked) found a mean difference from reference of -0.51 bpm on the treadmill, against -4.55 bpm in cycling and -7.26 bpm in resistance training. Averages like that hide big individual errors, and the models tested are largely gone. The direction is the point: gym and bike sessions are harder.

Polar's manual says the same in its own way. It recommends a chest strap where the sensor can't stay still, or where muscles and tendons move near it. Why wrist heart rate fails in hard sessions has the full evidence, including the gap: I found no large independent test of current flagship watches in real intervals.

Step 6: add a strap if it matters

A chest strap is the better choice when accuracy matters. In Gillinov's 2017 peer-reviewed study of 50 healthy adults (abstract read, funding unchecked), a Polar H7 strap reached rc 0.996 against ECG, and the wrist and forearm devices ran from 0.92 to 0.67. Those are decade-old models, so the ranking among them doesn't apply to today's watches.

Straps have their own fit routine. Polar says to moisten the electrode areas, fasten it snugly and check the electrodes sit firmly against your skin. If readings go odd, a Garmin Forerunner 945 LTE manual suggests reapplying water to the electrodes, tightening the strap and warming up for 5 to 10 minutes.

If you won't wear a chest strap, try an upper-arm sensor. Schweizer and colleagues (2025, peer-reviewed; no conflicts declared) tested 16 adults, mean age 27.4, across 9 activities from lying down to HIIT, with a Polar H10 as reference. A Polar Verity Sense on the upper arm had 1.43 bpm mean absolute error, against 6.41 bpm for a Polar Vantage V2 on the non-dominant wrist. All Polar, all small, and the data were cleaned of artefacts first, so it's a pointer. Don't assume it holds for other brands.

Tattoos and skin tone

Polar's manual says to avoid placing the sensor right on a wrist tattoo. That's sensible and it's as far as anyone can go, because I found no peer-reviewed tattoo study on a wrist-worn watch.

The one study I found used an armband. Navalta and colleagues (2025, peer-reviewed, Sensors) tested a Polar Verity Sense on 25 people against a chest strap. Error over tattooed skin at rest was 22.9%. Once the sensor's dropouts to zero were removed, it was 4.2%. So: try the other wrist if you have a tattoo there, and don't expect certainty.

On skin tone, the evidence is unsettled. Koerber and colleagues (2023, peer-reviewed review, 10 studies, 469 participants) found 4 studies showing lower accuracy on darker skin, 4 showing no effect and 2 mixed, and they call it preliminary and inconclusive. If your watch reads oddly at steady effort after these steps, cross-check against a strap. That's a reasonable test whoever you are.

A quick way to check yours

Wear a strap and the watch together on a steady 20-minute run, then look at both traces afterwards. If they sit together, your watch is probably fine for that kind of session on that firmware. Repeat with intervals. This is a check for you, not a study, but it's better evidence about your wrist than anything else I can offer.

To do that, you'll need to connect a chest strap to your watch, and bear in mind the watch may then show the strap's number. Run the strap on a second device if you can. How optical heart rate works explains why the fit matters, and the strap and sensor catalogue lists what's out there.