How accurate are fitness trackers and step counters?

What is the most accurate fitness tracker?

There isn’t one best at everything. A review of 158 studies found trackers accurate for steps and heart rate in the lab. But how accurate varied by brand and model.

Calories were the weak spot. For calories burned, the same review found no brand was accurate.

Think of steps like a fuel gauge. It won’t tell you the exact litre, but it can tell a 4,000-step day from a 9,000-step day.

Your exact model may never have been checked. Only about 11% of 310 trackers released up to 2024 had been tested for even one measure.

So pick the number you’ll actually use, and judge a tracker on that one.

What is the most accurate step counter?

In lab tests, Fitbit, Apple Watch and Samsung appeared to count steps accurately. Apple and Samsung had the tightest results, but fewer studies tested them. Withings and Misfit kept counting too few.

Everyday life is harder than a lab. Out in the real world, fewer than half of step counts were close.

Where you wear it matters too. Experts writing in JAMA said results line up only if the device sits in the same place every day.

Check yours. On a normal walk, count 100 steps in your head and see what the tracker adds.

Why does my tracker miss steps when I walk slowly?

Slow steps are harder to spot. One study tested 6 trackers on 18 healthy people aged 65 to 74. Every tracker counted too few steps as walking got slower.

Below 2 km/h, wrist trackers can be badly out. In the same study, waist-worn devices gave more even results. An earlier study suggests the hip or ankle may suit older adults who walk unevenly.

So if you walk slowly, expect a low step count.

Count minutes too. The NHS asks adults aged 19 to 64 for at least 150 minutes of moderate activity, or 75 minutes of vigorous activity, a week. Moderate means you can still talk, but not sing.

See how many steps a day you need and walking pace versus step count.

Can I trust the calories my watch says I burned?

Not closely. One lab study tested 7 wrist trackers on 60 adults. The typical calorie error ran from 27% to 93%, depending on the device.

Sitting still was the worst.

In the big review, no brand was within 3% more than 13% of the time. Apple tended to count too many calories. Garmin tended to count too few.

So a 500 on your screen could be 100 or more out, either way. Treat the calorie number as a rough guide, not a meal plan.

Trying to lose weight? Use a calorie deficit calculator to plan food instead.

How accurate is heart rate on a fitness tracker?

Much better than calories. Across 24 reviews, trackers were about 3% out on average.

In one lab study, they did best on a bike and worst when walking: the typical error was 1.8% cycling and 5.5% walking.

By brand, Apple Watch was within 3% in 71% of tests. Fitbit managed 51% and Garmin 49%, and Fitbit tended to read low.

Want to know what your resting number means? See normal resting heart rate. For sleep scores, see how accurate sleep trackers are.

When to speak to a GP

A tracker can’t tell you what a symptom means. The NHS says to see a GP if you’ve had heart palpitations and feel well, but:

• they keep coming back or are happening more often
• they last longer than a few minutes
• you have a heart condition, or heart problems in your family
• you think you may have atrial fibrillation, a heart rhythm problem where your pulse is not steady

Call 999 or go to A&E if palpitations don’t go away, or come with chest pain, shortness of breath, feeling faint or fainting. Do not drive yourself to A&E. If those symptoms have stopped, call 111 or ask your GP surgery for an urgent appointment.