Is it possible to save up calories like Weight Watchers save

I think it's fine, but there is a limit. For me, if my calories balance out over a 3-4 day running average, I don't see any unexpected loses or gains. But when I was doing WW and I banked for 4-7 days, I don't think that really worked.

It takes while for the calories in your food to be completely processed. So anything you eat in the later part of the day probably hasn't hit your scales by morning. So it makes sense to me that our bodies are more of a conveyor belt when it comes to calories rather than a cycle where you have to balance very 24 hours. But 6 days of banking? That seems a bit much.

Some other facts to ponder:

There are studies showing that people who are very strict during the week but let loose on the weekend don't lose as well (or sometimes at all) compared to people who are more regular in their calorie restriction.

There is a school of thought that says that you need to vary your calories to get maximum weight loss. (Some call it calorie cycling; some call it zig-zagging.) The idea is to mix things up so your body doesn't think it's in the middle of a famine and lower your metabolism (as much).

So the one tidbit implies you can't bank over the course of an entire week while the other tidbit suggests you can. Though, the calorie cycling advice I've seen is to mix it up every 3-4 days, not 1-2 out of 7. This corresponds to my own experience that you can't bank all week for the weekend but you can bank for two days (sometimes 3) for a third (sometime 4th) day.

I don't see a problem. It works for me. My daily limit is 1000 calories, which is a net of 7000/week. I base my calories on my weekly net instead of a strict 1000 a day. On Saturdays I like to eat out and cook a nice breakfast and only having a 1000 limit just doesn't work on Saturdays. So, I workout more a few days a week to bank some extra calories for the weekend, but at the end of the week, I'm still at a net of 1000/calories a day or 7000 a week.