Extra calories saved up?

I routinely calorie bank now that I'm in maintenance (eat maybe 150-250 calories under maintenance some days, to eat more on others). Also, some people eat 500 (ish) calories 2 days a week, and maintenance calories the 5 other days (5:2 fasting), so strategies like that can work.

What I'd caution is to keep it in the realm of reasonable, on average. One week like you describe isn't a problem, probably, for most people. But consider the context, the overall picture. What's "reasonable" is personal.

A calorie deficit - any calorie deficit - is a physical stress. The bigger the deficit (the faster the loss rate), the higher the physical stress.

Some people, when dieting, add other forms of physical stress, like major shifts in what they're eating (which can temporarily be a physical stressor even if the new foods are more nutritious), or adding new and challenging exercise. Those are additional physical stresses on top of what may be in a person's routine daily life, such as a physically demanding job or family care responsibilities, poor sleep, health conditions, etc.

On top of that, physical stress conspires with psychological stress, in some ways. For many, there are psychological stressors in the weight-loss picture, too: Figuring out new ways of eating, maybe partner/family conflicts, social anxiety about the gym or just about exercise competence, habits of guilt or self-blame from eating so-called "bad foods" or eating past calorie goal, and more. Those are also on top of psychological stresses in a person's routine life, such as job conflict, coronavirus worries, home-schooling kids, financial problems, etc.

Some people are more resilient to stress than others. No one is infinitely resilient.

With high stress levels (from any/all sources), higher water weight fluctuations or water retention are possible (from stress hormones). Health consequences are possible. Also, problems with long-term calorie-goal compliance become more likely, because any one person has a limited store of resilience (as played out through "motivation" or "willpower" or whatever we want to call it).

So, yes: Eat that pizza, and enjoy it. But also think about the overall pattern of your life and eating, and think about whether you're managing all-source stress well. If it were every week, an extreme calorie deficit for 3 days, and a normal deficit for (say) 3, and then a big-eating day . . . well, it might be fine, but it might not be a good overall stress-management strategy, for long-term health, happiness and goal accomplishment. You know yourself best.

It's good to understand ourselves in ways like this, and be realistic, IMO.

Best wishes!

I'm not biting your head off, but if you are eating only half of the minimum recommended I encourage you to look at how to consume more calories, and NUTRITIOUS calories on a daily basis. Additional healthy fat and protein should help. While it's ok to bank a few calories (100-200 a few days) for a treat, if you're eating only half your calories I would not use it all on pizza. I LOVE pizza but its also important to balance out your nutrition for HEALTH reasons.