How to calculate observed TDEE from intake and weight change

Observed TDEE is a working estimate built from two signals: your average logged calorie intake and your smoothed weight change over time. If weight falls, the estimated energy represented by that change is added to intake; if weight rises, it is subtracted.

Formulas such as the Mifflin–St Jeor equation estimate resting energy needs from population data. An activity factor can turn that result into a useful starting TDEE, but it cannot capture every difference in movement, body composition, or changing circumstances.

Logged observations offer another useful—but still imperfect—signal. Research on dynamic body-weight models shows why weight responses to energy imbalance are not perfectly linear, and tools such as the NIDDK Body Weight Planner use more detailed dynamic modelling. The shorter equation below is a practical approximation for interpreting your own recent logs, not a clinical measurement.

The basic formula

The observed TDEE formula compares your average daily calorie intake against the change in your scale weight over a known period.

What this means in plain language: If your weight stays exactly the same, your observed expenditure matches your average intake. If your weight drops, your expenditure was higher than your intake (so we add the energy equivalent of that weight loss). If your weight rises, your expenditure was lower.

The 7,700 kcal/kg figure is a practical approximation representing the rough energy equivalent of one kilogram of human body tissue change. Calorie Curve's method uses this as a working constant to translate scale movement into energy data.

A worked example

Assume you have tracked your food and weighed yourself consistently over 20 days:

• Average Intake: 2,400 kcal per day
• Start Weight: 85.5 kg (smoothed)
• End Weight: 84.0 kg (smoothed)
• Span: 20 elapsed days

Using the formula:

Data requirements and the blend

If this math were applied to a single day, or even a few days, the result would be wildly erratic because scale weight fluctuates due to water retention and digestion. To make the output useful, Calorie Curve evaluates up to 21 recent days and imposes strict data thresholds before the calculation is even permitted:

• You must have at least 10 complete intake days.
• You need weigh-ins on at least 3 distinct dates.
• The elapsed span between the earliest and latest weigh-in must be at least 7 days, or 14 days for the Lifestyle weight-loss mode.

Even with those requirements, raw observations contain noise. Calorie Curve uses smoothed weight change (a moving average) rather than isolated daily readings. It also bounds any observed estimate to a plausible range of 1,200 to 5,000 kcal to prevent large logging errors from breaking your plan.

Crucially, we do not rely purely on the observed figure. Calorie Curve calculates a working TDEE by cautiously blending your observation with the baseline formula. The observed contribution starts at 35% when you first meet the minimum data requirements, and scales linearly up to 70% if you maintain 21 complete days. The remaining share always anchors to the stable formula.

Frequently asked questions

Sources and further reading

• Mifflin et al. (1990): a predictive equation for resting energy expenditure
• Hall et al. (2011): quantifying body-weight response to energy imbalance
• Hall et al.: a computational model for estimating energy intake during weight loss
• NIDDK Body Weight Planner

Next steps

Building an adaptive target takes a few weeks of consistent habits. If you want to dive deeper into how Calorie Curve constructs your plan, read our full methodology. If you just need a starting formula baseline today, use our free calorie calculator or build a free plan in the app.