TDEE Calculator
Your total daily energy expenditure, with every activity level shown so you can sanity-check the multiplier.
What TDEE is
Total daily energy expenditure is everything you burn in a day: your basal metabolic rate (the energy needed just to run the body) multiplied by an activity factor between 1.2 and 1.9. Eat your TDEE and your weight holds; eat 500 kcal under it and you lose roughly half a kilo a week. The BMR here uses Mifflin-St Jeor, the equation with the best track record for non-athletic adults.
The multiplier is the weak link
BMR is predictable within about ±10%, but people routinely pick an activity level one notch too high. Training 4 times a week does not make a desk worker 'very active'; the factor covers your whole day, not your best hour. When between two levels, pick the lower one, run with the number for 3 weeks, and adjust from what the scale actually does.