someone asked me if i can save calories from one day to use to eat more the next day.. i have no clue but hope i can if i under eat 500 calories today could i eat 500 extra calories tomorrow or does it not work like that and i would gain weight etc?

My experience with under/over calories per day is ok once in a while as technically our bodies can't tell time as far as when one day starts and another ends. I just wouldn't make a habit of it (ie., don't hold back 500 calories for 4 days in a row so you can have 2000 extra on the 5th day, know what I mean?).

You didn't say what your daily calories are but I assume 500 is a significant chunk of food you'd be missing a day if it happens often.

Hope this helps!

yeah darn. i eat 1670 cals a day so saving up 500 would mean my body would go into starvation mode right? and just halt any weight loss? i have 664 cals left because i was busy all day and just got to eat now and its almost bedtime and i dont feel like eating more, should i eat anyways so my body doesnt go into starvation mode or its fine to do every now and then without going into starvation?

usually i dont think i will try to bank up calories since i forgot about the starvation thing

What you're describing is a form of calorie cycling. Generally people have a set number of calories a week (rather than a daily goal) and split it up amongst the days as they see fit. One might have one low day, a high day, etc.

I don't really calorie cycle, but when I have an occasion coming up (a holiday or vacation) I usually "save" my calories up by cutting back for a few days

Healthy well-adjusted eaters do this all the time. You might have heard someone on Thanksgiving say "wow I ate way too much today, tomorrow I'm only eating salad," or "I'm just having a yogurt for lunch today because hubby is taking me out to a fancy restaurant tonight and I'm saving my appetite." For binge eaters like me every day is Thanksgiving lol, but I do believe that what you describe is a normal fluctuating eating style, a style that I'm trying to achieve myself.

You will not hit starvation mode if you do this once in awhile. Starvation mode happens when you cut your calories very low and continue this for an extended period of time.

I agree with bargoo, if it happens once in a while you will not hit starvation mode.

But "saving" 500 from your 1670 very often I think would make you quite hungry on those days! In regards to the 664 you had left yesterday, there are posts on this site and myfitnesspal that will tell you how to get the calories in with little food (such as peanut butter for example) but I don't know enough about it to post it here. But for 1 day, it's not going to hurt you!