when does the calories for the day start and end?

okay so last night i had a big snack but it technically went on todays calories because it was after midnight, so do those calories count for today or yesterday?

I would say they count for TODAY.   Midnight to midnight is the way I define a day.

Your daily burn total on CC resets at midnight, but basically its up to you if you want to count them to todays total. Personally, I would forget about it, count it as a slip and not punish myself for the rest of the day for it and just try to do better.

start when you wake up, end when you go to sleep

i agree with christine... even if its 2am if youre awake... its still the same day i think.

ZOMG yes.  I mean people around here are always ordering like Chinese take-out at 3 AM.  I always count as the same day until I go to sleep.