Does carrying my phone in a bag lower my step count?

Yes, measurably. In the seven-day study, people who kept the phone in a pocket lost 791 steps a day against the reference pedometer; people who kept it in a bag lost 2,104. That is a difference of about 1,300 steps a day from the bag alone. Carrying frequency mattered even more: 929 steps lost for people who almost always had the phone on them, against 3,036 for people who seldom did.

Why does my iPhone miss steps when I walk slowly?

A step is recognised from a peak in acceleration, so a slow or shuffling stride can stay under the threshold and never register. Measured across step counters, error grows sharply as pace drops: roughly 9 to 12% at a person's own comfortable pace, 27% at 0.8 m/s, 52% at 0.6 m/s and 76% at 0.4 m/s. Those figures come from studies of worn pedometers rather than iPhones specifically, but the mechanism is the same one every accelerometer-based counter uses.

how accurate is the iPhone step counter?

Q: How accurate is the iPhone step counter?

It depends on what you compare it against. Over seven days of ordinary life, 54 adults carrying an iPhone recorded 9,253 steps a day against 10,530 on a validated pedometer — about 12% low. In a separate trial the same phone was within 5% on a treadmill and 21.5% low in free living. Measured against an ankle-worn StepWatch, an iPhone was 27% low — but a research-grade hip accelerometer in that same study was 28% low. Every device in that comparison underestimated by more than 20%, so the honest answer is that the gap depends on the reference, on how fast you walk, and on where the phone is.

Q: Is the iPhone or the Apple Watch more accurate for steps?

The Watch counts more of your steps because it is on you all the time, which is the real difference — not a better algorithm. But it is not a source of truth either. In the Framingham Heart Study, 523 people wore an Apple Watch alongside a research-grade hip accelerometer for 3,223 days: the two agreed within 15% on only 29.7% of days, and the limits of agreement ran from 9,543 steps below to 8,544 above. The low error figures you see quoted for the Watch come from treadmill studies, not from ordinary life.

Q: Do newer iPhones count steps more accurately?

Nobody has published a comparison. Studies that list handsets pool several generations into one sample rather than treating the model as a variable, which suggests the researchers did not expect it to matter. That is not proof that no difference exists — it means it has not been measured. The differences that have been measured are much larger: pocket against bag is about 1,300 steps a day, and walking pace changes the error several times over.

Close enough to trust the shape of your day, and looser than you'd guess about the total. Over a week of ordinary life an iPhone runs about 12% low against a validated pedometer — and the honest version of the answer starts with a second question: accurate compared to what?

What the studies measured

Three published trials, three different references, one phone. Read the last column as a shortfall: how many steps the phone did not report.

Measured iPhone step count error, by condition and reference device. Sources: Duncan et al. 2018, JMIR mHealth 2019, three-day StepWatch trial.
condition	reference	shortfall
Treadmill, 5–10 km/h	hand-counted steps	under 5%
7 days, 54 adults	validated pedometer	12%
Free living, same trial	accelerometer	21.5%
3 days, 29 adults	ankle StepWatch	27%

The 12% figure is 9,253 steps recorded by the phone against 10,530 on the pedometer — 1,277 missing a day. The free-living figure is about 1,340 a day.

Accurate compared to what

Those four rows look like a phone getting worse. They are four different questions.

The last study is the one that settles it. Twenty-nine people wore an iPhone, two wrist trackers and two research-grade hip accelerometers against an ankle-worn StepWatch for three days. The iPhone was 27% low. The research instrument on the hip — the kind used to validate everything else — was 28% low. Every device in that comparison underestimated by more than 20%, and the authors say so plainly.

So the phone is not uniquely bad at this. Counting steps in real life is a hard measurement, and any single figure you read is really a statement about a pair: this device, against that reference, in those conditions.

Where you keep it matters more than which iPhone you own

The seven-day study split its participants by habit, and this is the part worth acting on. Same phones, same week — different pockets.

Steps missing per day, by how people carried the phone (JMIR mHealth, 2019)
how it was carried	steps missing per day
In a pocket	791
In a bag	2,104
Almost always on you	929
Sometimes on you	1,424
Seldom on you	3,036

A pocket instead of a bag is worth about 1,300 steps a day. Carrying the phone at all is worth more than 2,000. No app can recover a step the phone never felt — which is why the fix for a low count is a pocket, not a different download.

Why a slow walk goes missing

A step is recognised from a peak in acceleration. A slow, flat, shuffling stride can stay under that threshold, and a step that never crosses it was never counted. Error grows steeply as pace drops: roughly 9–12% at a comfortable pace, then 27% at 0.8 m/s, 52% at 0.6 m/s and 76% at 0.4 m/s.

Those figures come from studies of worn pedometers rather than iPhones specifically. The mechanism is shared by every accelerometer-based counter, but the numbers belong to those devices, not to your phone.

Is an Apple Watch more accurate?

It catches more of your steps, and the reason is duller than it sounds: it is on you the whole time, and your phone is not. That is a difference of exposure, not of cleverness.

It is also not a source of truth. In the Framingham Heart Study, 523 people wore an Apple Watch alongside a research-grade hip accelerometer for 3,223 days. The two agreed within 15% on 29.7% of days, and the limits of agreement ran from 9,543 steps below to 8,544 above. The single-digit error rates quoted for the Watch come from treadmill trials. Checking your phone against your watch swaps one instrument's blind spots for another's.

Do newer iPhones count better?

Nobody has published a comparison. The trials that list handsets pool several generations into one sample instead of treating the model as a variable — researchers did not expect it to matter. That is not proof that no difference exists; it means it has not been measured.

Meanwhile the differences that have been measured are much larger than any plausible gap between generations: about 1,300 steps a day between a pocket and a bag, and several-fold changes with walking pace. The question is worth asking about your habits, not about your handset.

What this means for the number on your screen

Steps are an estimate, and they always were. What makes them useful is not being exact but being consistent: the same instrument, carried the same way, compared with itself. A day that reads higher than yesterday really was a longer day.

Angel Step reads the figure Apple Health already holds and never keeps a count of its own, so there is no second opinion to reconcile — which is the practical lesson of all four studies above. If two counts disagree, why your step counts don't match explains which one Health keeps and why. If yours has stopped moving entirely, that is a different problem with a shorter answer.

Sources

Duncan et al. (2018), Journal of Sports Sciences — treadmill and free-living validity of the iPhone Health step count. PubMed
Höchsmann et al. (2019), JMIR mHealth and uHealth — 54 adults, seven days, carrying habits. JMIR
Three-day free-living comparison against an ankle-worn StepWatch, including two research-grade hip accelerometers. PMC
Framingham Heart Study (2024) — Apple Watch against a research accelerometer in a community setting. PMC
Pedometer accuracy in slow-walking older adults. PubMed
Apple, Core Motion — the motion coprocessor records movement in the background and keeps seven days of history. Apple Developer