Adaptive TDEE Calculator
Every formula on this site predicts your TDEE from your body size. This adaptive TDEE calculator does the opposite: it takes what you actually ate and what your weight actually did, and works backwards to a rough average of what you burned over that period.
How the adaptive TDEE calculator works
A kilogram of body mass change is treated as roughly 7700 kcal. That is a simplification: early weight change is partly water and glycogen, which carry far fewer calories than fat. If your weight fell over the period, you ate that much under your real TDEE; if it rose, you ate over it.
Estimated TDEE = average daily intake - (weight change kg x 7700 / days)Step 1 - Weight change
69.4 - 70 = -0.6 kg (lost)Step 2 - Convert to a daily surplus or deficit
-0.6 x 7700 / 21 = -220 kcal/dayStep 3 - Add it back to intake
2400 - (-220) = 2620 kcal/dayYour estimated average TDEE
2620 kcal per day
Intermediate values are exact unless marked with ≈; only the final result is rounded to a whole number.
A worked example
The defaults describe 21 days of tracking at an average of 2400 kcal a day, with weight going from 70 kg to 69.4 kg. The change is -0.6 kg, which is about 4620 kcal (0.6 x 7700). Spread over 21 days, that is a deficit of 220 kcal a day. Add it back to intake and the estimated average TDEE is 2400 + 220 = 2620 kcal/day.
Compare that with a formula. If the same person's Mifflin-St Jeor estimate were 2450, the data would be saying they burn about 170 kcal more than the formula assumed - a common outcome for people who move more during the day than the activity level they picked.
Why formulas drift
Predictive equations assume an average person and an activity factor you picked yourself. Metabolism varies between people of identical size, and the activity multiplier is the biggest guess in the whole calculation. Your own data replaces that guess with what actually happened - though it brings its own noise, covered below.
How to collect data that gives a usable answer
- Weigh every morning, after the bathroom and before eating or drinking, on the same scale in the same place.
- Use averages for the start and end weights: the mean of the first three to five mornings and of the last three to five. A single weigh-in can swing by a kilogram on salt, carbohydrate or a late meal.
- Log everything, including cooking oil, drinks and weekend meals. Missed items do not cancel out; they all push the result the same way, making your TDEE look lower than it is.
- Keep the window ordinary. Illness, travel or a big change in training adds water-weight noise. If you menstruate, a window of about four weeks evens out cycle-related water retention.
Read this before trusting the number
Track at least 14 days, ideally 21. Shorter windows are dominated by water weight, glycogen and gut contents rather than fat. A 1 kg error in either weigh-in moves a 14-day result by 550 kcal a day, so weigh under the same conditions each time and use the average of a few mornings for the start and end weights. The result is also only as good as your intake logging, which most people underestimate.
When to run the adaptive TDEE calculator again
TDEE is not fixed. As you lose weight, a smaller body burns less, and during a long diet energy expenditure can drop a little further than size alone explains. As you gain, the reverse. A prediction formula only notices those changes when you update your inputs; an adaptive TDEE calculator picks them up from the data.
A practical rhythm is to rerun it every three to four weeks while dieting or gaining, using only the latest window of data, and to adjust intake by the difference. During maintenance, once every month or two is enough.
Starting out and have no data yet? Begin with the Mifflin-St Jeor calculator.