A worked example
Eating 2,200 kcal a day on average while going from 82 to 81 kg over 28 days is a deficit of about 280 kcal a day, so the body was burning around 2,480 kcal.
How the calculation works
A kilogram of body weight lost or gained is taken as roughly 7700 kcal, the figure Hall (2008) examines. Multiply the change by 7700, spread it over the days, and you have the daily gap between what you ate and what you burned. Add that gap back to what you ate and you get the burn.
Nothing here depends on an activity level or a formula fitted to other people, which is the whole point. If your job is more active than it looks or your metabolism runs a little slow, the result already includes it.
What a weekly change means per day
Read it either way. Losing half a kilo a week takes a gap of about 550 kcal a day, and if the scale says you’ve been losing that fast, you’ve been eating about that much under your burn.
| Per week | In pounds | kcal a day |
|---|---|---|
| 0.1 kg | 0.2 lb | 110 |
| 0.25 kg | 0.6 lb | 280 |
| 0.5 kg | 1.1 lb | 550 |
| 0.75 kg | 1.7 lb | 830 |
| 1 kg | 2.2 lb | 1,100 |
Getting numbers you can trust
Daily weight jumps by a kilogram or more on salt, carbs and water, so single weigh-ins make this noisy. Weigh most mornings and use the average of the first week and of the last week. Log honestly, including the bits that feel too small to count, since the result can only be as good as the intake figure.
Two weeks is the least that gives a usable answer and four is better. Over a very long stretch, if your weight changed a lot, your burn changed with it, so the result is an average across the period.
Questions people ask
Why is my result so different from the TDEE formula?
Formulas describe an average person of your size. Real burn differs by a few hundred calories either way from things a formula can’t see, such as how much you move without noticing. When the two disagree and your log is honest, trust the log.
Is 7700 kcal per kilogram exact?
No. It depends on how much of the change is fat and how much is lean tissue and water, and it varies between people. It’s the standard working figure and good enough for a trend over weeks.
What if I didn’t track every day?
Use the average of the days you did track, but only if they were typical. Skipping the busy weekends and logging the careful weekdays makes intake look lower than it was.