How Tare calculates your real TDEE
Every calorie target rests on one number: your Total Daily Energy Expenditure. Most apps estimate it once, from a formula, and never check. Tare measures it — from your own weigh-ins and your own food log — and this page explains exactly how.
The problem with formulas
Mifflin-St Jeor, Harris-Benedict, Katch-McArdle — every TDEE formula is a regression over a study population. They are good averages and poor individuals: for a given person they can miss by several hundred calories, because metabolisms differ for reasons no age-height-weight equation sees. Worse, a formula has no feedback loop. Eat at your "deficit" for two months with no result, and the formula keeps insisting the deficit exists.
The measurement that is always available
You do not need a lab or a wearable to measure expenditure, because energy balance leaves evidence: the difference between what you eat and what you burn appears on the scale. If intake is known and weight change is known, expenditure is the only unknown left — arithmetic, not estimation.
The catch is that raw scale weight is noisy. Water, sodium, and digestion move it by more in a day than body fat changes in a week. So Tare first smooths your weigh-ins with an exponential moving average into a trend line, and everything downstream reads the trend, never a single weigh-in.
A worked example
Suppose you log 2,000 calories a day and your weight trend falls 0.5 kg per week. Half a kilogram of tissue is roughly 3,850 calories, or about 550 per day. Your real expenditure is therefore about 2,000 + 550 = 2,550 calories — whatever any formula predicted. If your goal is to keep losing at that rate, your target stands; if you are losing faster than intended, the target comes up. The update runs weekly, from your trailing 28 days.
Three phases, four weeks
- Days 0–13
Formula only
Mifflin-St Jeor with an activity multiplier — the same estimate every calculator gives. There is no data yet, so a population average is the best available answer.
- Days 14–27
Blend
The measured value starts to exist and earns weight daily. The formula’s share shrinks as the trend line firms up.
- Day 28 onward
Fully adaptive
The formula is retired. Your TDEE is back-calculated entirely from your own weigh-ins and food log, updating weekly from the trailing 28 days.
Guardrails
A measured system needs limits a formula does not. Tare caps how far a single weekly update can move your target, so one strange week — travel, illness, a water-weight swing the smoothing could not fully absorb — cannot whipsaw your plan. The weekly check-in shows you the suggested change before it applies; nothing moves without you accepting it.
What the Apple Watch adds — and doesn't
Nothing above requires a wearable. With an Apple Watch, the optional Activity Bonus adjusts a single day: when your recorded active energy exceeds your typical day, the surplus is added to today's target as it happens — upward only, so a rest day never shrinks your budget. The weekly TDEE remains owned by the weigh-in math.
Try the starting point
The free browser calculator runs the same Mifflin-St Jeor starting formula the app uses in its first two weeks — useful as a first estimate, and a demonstration of exactly what the adaptive system exists to replace. The full mechanics, including the weekly check-in and the calibration progress indicator, are in the docs.
Common questions
How can an app know my TDEE without a fitness tracker?
From arithmetic, not sensors. Energy balance means the gap between what you eat and what you burn shows up on the scale. Tare smooths your weigh-ins into a trend, compares that trend against your logged intake, and solves for the only unknown — your expenditure. If you eat 2,000 calories a day and your trend falls half a kilogram a week, you are burning roughly 2,550. No wearable is required; an Apple Watch only adds the optional Activity Bonus on top.
My weight jumps around day to day. Does that break the estimate?
No — daily jumps are mostly water, sodium, and digestion, and Tare never uses a single weigh-in directly. An exponential moving average smooths the series into a trend line, and the TDEE calculation reads the trend, not the scale. What helps most is weighing in regularly, at a consistent time of day.
How long until the target is accurate?
About four weeks. The first two weeks use a standard formula (Mifflin-St Jeor with an activity multiplier) because there is not enough data for anything better. Weeks three and four blend the formula with the measured value as confidence grows. From day 28 the formula is retired and the target updates weekly from your trailing 28 days of data.
What if I forget to log some meals?
The estimate is only as honest as the log. Unlogged food makes measured expenditure look lower than it is, which lowers your target. Occasional gaps wash out over the 28-day window; systematic under-logging does not. This is true of any adaptive system — the difference is that Tare is measuring you, so what you feed it matters.
Is this the same as the calculators on the web?
Only for the first two weeks. Web calculators are the formula — a population average that can miss an individual by hundreds of calories and never finds out. Tare uses the formula as scaffolding, measures the real number, and takes the scaffolding down. You can try the starting formula in the free browser calculator; the adaptive part needs your data over time.
Last reviewed against Tare v1.13.0.
Stop guessing your burn
Four weeks of ordinary logging, and your target comes from your body.