APPLE WATCH / IPHONE / ACCURACY

Is Apple Watch or iPhone more accurate for counting steps?

Both are accurate enough for daily tracking at normal walking speeds, and neither is perfect. Lab studies found Apple Watch step counts very close to hand-counted steps, and smartphone apps within about 7% of observed steps. The bigger difference is what each device sees: your iPhone misses steps when it is not on you, and your watch can miss steps when your arms are still.

By the Upmoat studio · Published October 3, 2026 · Last updated October 3, 2026

Key takeaways

In one lab study, Apple Watch recorded 2,964 steps vs 2,965 counted on video (Veerabhadrappa et al., 2018).
In a JAMA test, smartphone apps were within −6.7% to +6.2% of observed steps, while wrist wearables ranged from −22.7% to −1.5% (Case et al., 2015).
Trackers are generally less accurate at slow walking speeds (Fokkema et al., 2017).
The phone misses steps when it is on a desk; the watch can miss steps when you push a trolley or pram.
Apple Health merges both devices without double counting, using your Data Sources priority.

What do accuracy studies show?

Several independent lab studies have compared iPhone apps and Apple Watch with steps counted by hand or on video.

Step-count accuracy studies involving phones and Apple Watch
Study	Setup	Result
Case et al., 2015 (JAMA)	14 adults, 56 treadmill trials at 3.0 mph; 10 apps and devices	Smartphone apps: −6.7% to +6.2% vs observed. Wearables: −22.7% to −1.5%
Fokkema et al., 2017 (Med Sci Sports Exerc)	31 adults, 10 trackers incl. Apple Watch Sport, three speeds	Accuracy depended on speed; Apple Watch among the most accurate at average and vigorous pace
Veerabhadrappa et al., 2018 (J Gen Intern Med)	Apple Watch vs video-counted steps at different speeds	2,964 vs 2,965 steps on average: described as extremely accurate

Two caveats. These are small studies using older hardware, and treadmill walking is tidier than real life. They do show that, at normal speeds, both kinds of device count steps well; the bigger errors come from how and when you carry them.

Why does the iPhone miss steps?

An iPhone can only count steps while it is moving with you. Common reasons it reads low:

It sits on your desk, kitchen bench or charger while you move around.
It is in a bag that swings or rests on a trolley.
You are on a treadmill or walking pad holding a rail, with the phone on the console.

When it is in a trouser pocket, it is close to your centre of mass, which suits step detection well.

Why does Apple Watch miss or add steps?

A watch counts from wrist movement, so it can under-count when your arm is still while you walk, such as pushing a pram, shopping trolley or holding a rail. It can occasionally register arm movements that are not steps. Apple recommends calibrating your watch by walking or running outdoors with your iPhone to improve distance and pace accuracy (Apple Support).

Which device sees which steps
Situation	iPhone	Apple Watch
Phone left on desk, walking around office	Misses steps	Counts steps
Pushing a pram or trolley	Counts if in pocket	May under-count
Treadmill, holding the rails	Counts if in pocket	May under-count
Phone in pocket, arms swinging	Counts steps	Counts steps
Very slow shuffling	Less accurate	Less accurate

What happens in Apple Health when both record the same walk?

Apple Health does not simply add the two numbers. When more than one source records the same type of data, Health uses the source higher in your priority list for overlapping periods. By default, data you enter manually ranks first, then data from your iPhone and Apple Watch, then apps and Bluetooth devices (Apple Support). You can reorder sources in Health › Browse › Activity › Steps › Data Sources & Access › Edit.

That is why a single device can show a different number from Health’s total. We cover the data side in more detail in why iPhone and Apple Watch step counts differ.

Which step count should you trust?

Use Apple Health’s combined total as your daily number. Apps that read from Health, including StepIsland, show that merged total.
Wear the watch if you have one. It is with you even when the phone is not.
Pick one source of truth and stick to it. Day-to-day trends matter more than small absolute differences.
Do not chase exact numbers. A few percent either way makes no practical difference to a goal like 7,000–10,000 steps a day.

Frequently asked questions

Is Apple Watch accurate for steps?

Yes, at normal walking speeds. A 2018 study found Apple Watch step counts almost identical to steps counted on video, and a 2017 study ranked it among the most accurate trackers at average and vigorous walking speeds.

Is the iPhone accurate for steps?

When it is carried on your body, generally yes. A 2015 JAMA study found smartphone apps within about 7% of observed steps on a treadmill. It misses any steps taken while the phone is not on you.

Why do my Apple Watch and iPhone show different steps?

Each device counts steps from its own sensors and only while it is moving with you. Apple Health then merges the two by priority without double counting, so each device’s own number can differ from the Health total.

Does Apple Health double count steps from iPhone and Apple Watch?

No. When sources overlap, Apple Health uses the higher-priority source for that period rather than adding both together.

How can I make my step count more accurate?

Wear your Apple Watch, carry your phone in a pocket rather than a bag, calibrate the watch with an outdoor walk with your iPhone, and keep your Health data source priorities sensible.

From the studio behind this journal

See your combined Apple Health steps grow a little world.

StepIsland is Upmoat’s walking app and step counter for iPhone and Apple Watch. Pick a companion, set a goal and watch an illustrated world grow with your Apple Health steps, live on your Lock Screen, Dynamic Island, widgets and Apple Watch.

Explore StepIsland

Sources