Two numbers, not one#
Apple Health keeps burned energy in two separate buckets, and almost every confused question about it comes from treating them as one.
- Resting energy — the cost of being alive at rest. In Health this is written almost entirely by an Apple Watch. An iPhone on its own does not produce it.
- Active energy — the extra from movement. An iPhone does produce this, from its motion sensors and step counting.
So on an iPhone with no Watch, Health typically has active energy and no resting energy. Your total expenditure is not sitting there waiting to be read; half of it is missing.
Health also stores dietary energy — calories consumed — but only because some app wrote them there. Health does not count food. Something has to log it.
What happens when you are not wearing the Watch#
Nothing is generated for the hours it was off your wrist. There is no retrospective fill and no estimate: Health records what was measured, and an unworn Watch measures nothing.
The consequence is that a day with the Watch and a day without are not comparable numbers, even though both appear in the same chart. This is worth knowing before drawing a conclusion from a week that contains both.
The same applies in low-power states — what gets recorded depends on which sensors are still running, and it will not match a normal day.
How accurate is any of it?#
Resting energy from a Watch is itself a formula — Apple estimates it from your profile, not from measurement, so it inherits the same population scatter as any other basal-rate equation. Active energy is estimated from motion and heart rate, which is better than nothing and worse than a laboratory.
The honest summary: Health’s expenditure figures are a decent relative signal and a poor absolute one. Useful for comparing your Tuesday to your Thursday. Less useful as the literal number of calories you may eat.
What SmartCrunch does with it#
Health is optional throughout — the app works with it switched off — and the exchange is deliberately narrow.
It reads body mass and body composition, height, energy, dietary entries and a handful of related channels, so that a weight typed into any app shows up on the same trend line here.
It writes exactly four things: the day’s total energy, protein, carbohydrate and fat. Nothing else is ever written.
There is one rule worth knowing, because it prevents a bug that would otherwise be invisible: the app never reads back the channels it writes. Its own samples are excluded when it queries Health, so the four totals it exported this morning cannot return as a second set of entries and count your breakfast twice.
Health is also woven into the ladder the app uses to establish your maintenance. Rung two is Health’s own measured history — but as explained above that rung needs a Watch, so a phone-only user never reaches it. That is precisely why rung three exists: a formula’s basal rate plus your measured active energy from Health. Half a measurement beats none, and the ladder used to throw that half away.
The practical answer#
- You have a Watch and wear it most days. Health’s expenditure is a reasonable input, and the app will use it — while preferring, once you have logged a few weeks, to solve your maintenance from your own data instead.
- You have an iPhone only. Health gives you active energy and your weight history. That is genuinely useful and it is not a total expenditure figure.
- Either way, do not eat back exercise calories. In this app they never appear as a bonus to spend; activity reaches the number through expenditure on the rungs that measure it, which is a different thing and a much less error-prone one.
Read next
- Maintenance calories, explained Maintenance is the intake at which your weight holds. Every calculator predicts it from a population; your own logged weeks can measure it instead.
- What is TDEE, and why do calculators disagree? TDEE is maintenance under another name. The disagreement between calculators is almost entirely the activity multiplier, and it is the part no form can know.