Adaptive TDEE is your maintenance calories measured from your own data instead of a formula. The method: observed TDEE = average daily intake − (weight trend slope × 7,700 kcal per kg, about 3,500 per lb). If you eat 2,000 kcal a day and your trend falls 0.5 lb a week, your observed TDEE is about 2,250 kcal. It needs roughly two to four weeks of logs.
Key takeaways
- Adaptive TDEE equals average intake minus the weight trend slope times about 7,700 kcal per kg (3,500 per lb), so it needs both weight and intake logs.
- A least-squares trend line through all weigh-ins is far more reliable than comparing two single weigh-ins, which water swings can distort by hundreds of calories a day.
- Plan on at least 14 days, ideally 28 or more, with most days weighed and logged.
- Logging errors pass straight into the result: if you under-log intake by 200 kcal a day, your adaptive TDEE reads 200 kcal too low.
How this adaptive TDEE calculator works
Paste a log with one day per line in the form weight, calories. Either value may be blank for a day. Commas, tabs and spaces all work, and blank lines and lines starting with # are ignored. The box is prefilled with a realistic 28-day example so you can see the output first.
The calculator returns your observed TDEE with an uncertainty range, a confidence rating (low, medium or high) and what more data would change, your average intake, your weight trend in change per week, and how many weigh-ins and intake days it counted. A chart shows each daily weight as a dot with the least-squares trend line through them. If you add an optional profile (sex, age, height, activity), it also shows the formula TDEE and the difference between the two.
What is adaptive TDEE and how is it calculated?
Energy balance says the change in your stored energy equals what you eat minus what you burn. If you know what you ate and how your weight changed, you can solve for what you burned:
Observed TDEE = average daily intake − (trend slope × 7,700 kcal per kg) Slope in kg per day; in pounds, use about 3,500 kcal per lb.
Losing weight means the slope is negative, so subtracting it adds calories back. The 7,700 kcal per kg figure is the usual approximation for the energy in a kilogram of body-weight change, and the weight-change rule it comes from has known limits over long periods (Hall et al., 2011; Thomas et al., 2014). Over the 2–8 weeks an adaptive estimate uses, it is a practical approximation.
If the same trend came with 1,800 logged kcal, the result would be 2,050; with 2,200 it would be 2,450. The weight slope stays fixed, so each logged calorie moves the answer one for one. That is why intake logging accuracy matters as much as the scale.
Why use a trend line instead of two weigh-ins?
Your scale weight moves with water, glycogen, sodium and digestion, and day-to-day swings of a pound or more are common, and body weight follows a weekly pattern, highest after the weekend (Turicchi et al., 2020). Compare a Monday weigh-in to a Monday two weeks later and a 2 lb water difference becomes an error of 2 × 3,500 ÷ 14 = 500 kcal a day.
A least-squares trend fits one straight line through every weigh-in in the window. Noise above and below the line averages out, so the slope reflects the real direction of fat and lean mass much better than any two points do. The more weigh-ins you have, and the longer the window, the smaller the uncertainty.
How many days of data do you need?
| Window | Weigh-ins | What to expect |
|---|---|---|
| Under 14 days | Any | Low confidence; the slope is mostly water noise |
| 14–27 days | 10 or more | Medium confidence; usable for a first adjustment |
| 28 days or more | 20 or more | High confidence; the steadiest estimate |
These thresholds are the ones this calculator uses to rate confidence. They are practical guidelines rather than a published standard. The estimate improves further when intake and weight are both logged on most days and your eating is fairly consistent.
How accurate is the result?
An adaptive estimate is only as good as its inputs. Three things matter most:
- Logging accuracy. If you under-log by 200 kcal a day, the result reads 200 kcal low. Self-reported intake can easily run low, so weigh food where you can.
- Stable conditions. Weigh at the same time of day, such as after the bathroom and before eating, and keep sodium and carb intake roughly steady.
- Enough time. A short window exaggerates noise.
It is also a snapshot. After a long diet your expenditure may be lower than a formula would predict (Rosenbaum & Leibel, 2010), and a measured estimate picks that up where an equation cannot. Compare the result with your formula TDEE; if they differ by more than about 10%, trust the data but check your logging first.
Why does adaptive TDEE change when I change my calories?
Because it is calculated from what you ate. If you raise your intake and your weight starts rising, the weight slope moves up and your measured TDEE stays near your true maintenance, which is the point. Early on, though, the estimate can overshoot. Bigger meals add water and food weight before any fat is gained, and a lower intake sheds glycogen and water first, so the first week after a change often overstates the shift. Wait one to two weeks before trusting the new number.
How does the TDEECalc app do this?
The TDEECalc iPhone app learns your adaptive TDEE every week from the weight and intake you log. Connecting Apple Health is optional and read-only. The app is free, has no account or ads, and keeps your data on your device. See the TDEECalc app for details.
This page’s calculator is the same idea for a one-off paste. If you want it without logging in a spreadsheet, the app does the arithmetic for you. How it compares with others is on the best adaptive TDEE apps page, and the method is explained at length in the adaptive TDEE guide.
What do I do with my adaptive TDEE?
Use it in place of the formula number. Set your calories relative to it: for example, a 10–20% deficit from your observed TDEE for fat loss. A starting calorie target from the calorie deficit calculator or the TDEE calculator can then be refined with your own numbers. Re-run it every few weeks, since weight loss, training and age gradually shift your expenditure.
Frequently asked questions
How is adaptive TDEE different from a TDEE calculator?
A TDEE calculator predicts maintenance from an equation using age, sex, weight, height and activity, so it gives an average for people like you. Adaptive TDEE measures your actual maintenance from your weight and calorie logs. It captures your real metabolism and habits, but only if the logs are accurate.
How long does adaptive TDEE take to work?
At least two weeks gives a rough estimate; four weeks or more gives a steadier one. This calculator rates confidence as low under 14 days, medium from 14 days with at least 10 weigh-ins, and high from 28 days with at least 20 weigh-ins.
Why does my adaptive TDEE change when I change my calories?
Weight takes time to respond to a new intake, and water and glycogen shifts can briefly distort the trend. Right after a big change, the estimate can swing. Give it another week or two of steady eating. A real change in expenditure can also occur after prolonged dieting.
Do I need to log every day?
No. Missing weigh-ins are fine because the line is fitted through the days you have. Intake is averaged over the days you logged, so skip days only when you can't log them reasonably accurately, and avoid logging only your good days.
Is there an adaptive TDEE app or spreadsheet?
Yes, several. The TDEECalc app does it automatically from your logged weight and intake, and a spreadsheet works with the same formula. See the best adaptive TDEE apps for an honest comparison.
References
- Hall KD, Sacks G, Chandramohan D, et al. (2011). Quantification of the effect of energy imbalance on bodyweight. The Lancet 378(9793):826–837.
- Thomas DM, Gonzalez MC, Pereira AZ, Redman LM, Heymsfield SB (2014). Time to correctly predict the amount of weight loss with dieting. Journal of the Academy of Nutrition and Dietetics 114(6):857–861.
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition 51(2):241–247.
- Rosenbaum M, Leibel RL (2010). Adaptive thermogenesis in humans. International Journal of Obesity 34(Suppl 1):S47–S55.
- Turicchi J, O’Driscoll R, Horgan G, et al. (2020). Weekly, seasonal and holiday body weight fluctuation patterns among individuals engaged in a European multi-centre behavioural weight loss maintenance intervention. PLOS ONE 15(4):e0232152.