How much of a deficit is too much?

Ainadan

Assuming you are eating at least your TDEE plus whatever for sedentary, at what deficit do you start eating calories back?

I teach 2 days a week (for 5 hours a day), and all in all, I burn around 800 to 1,000 more calories on those days than I do normally. So a 500 calorie deficit ends up being a 1,300 deficit. It isn't really exercise, so I don't know how to count it and my fitness tracker doesn't up my calories for it I don't think. Also, after 2 or 3 days of running a largish deficit, my body rebelled and I ate 400 more calories than I was supposed to, mostly in sugar. But before that I wasn't more hungry than normal.

estherdragonbat

How much are you trying to lose?

The main problem is that with too great a deficit, you'll lose muscle mass, as well. Your heart is a muscle.

In general, the way it works is:

If you have less than 15 lbs to lose 0.5 lbs/week is ideal. (250 calories/day deficit)
If you have 15 -25 lbs to lose 0.5 to 1.0 lbs/week is ideal (250-500 calories/day deficit)
If you have 25-40 lbs to lose 1 lbs/week is ideal, (500 calories/day deficit)
If you have 40-75 lbs to lose 1.5 lbs/week is ideal, (750 calories/day deficit)
If you have 75+ lbs to lose 2 lbs/week is ideal, (1000 calories/day deficit)

There are people with a lot more to lose who can go beyond the 1000/day, but usually they're under medical supervision.

Your body doesn't reset itself at midnight each night, so there's nothing wrong with, for example, having 80 lbs to lose, choosing to be in an 800 calorie deficit for five days of the week, and then having an extra 1,000 calories 'banked' for the weekend.

From what you're describing, it sounds like on those days, your activity level is lightly active. You might want to adjust your MFP settings to that and eat the extra calories. Or eat back a portion of the calories burned through exercise (start with 50% and see what that does).