Is there/will there be a seasonal sales calendar? I'd like to pu aside a budget tbh

The schedule is as follows:
"Whenever the GOG team feels like it, and can get permission from one or more publishers to sell their games for less."

I wouldn't expect any significant sale until June/July's summer sale.

There are two sales that pretty much always come at the same dates : summer sales around june/july, and winter sale around december.

These other sales come regularly with some variations year to year : insomnia sales in march, tower bundle promo (or some other kind) in april/may, some kind of sale in september (indie gamble thing, but that could change... they test many kind of sales all year round).

I may miss some other sales, there was a time where there was a big sale per month on GOG.

In recent years, the spring sale has been in early to mid March (the last two were Insomnia sales), the summer sale in June (and often lasting for two full weeks or longer), and fall and winter sales some time in November and early-ish December, respectively (generally with no more than two weeks between them). There's also usually a few smaller, themed sales interspersed throughout the year, but those can be a little harder to predict.

(And you shouldn't "pu" beside your budget, BTW -- it's extremely unsanitary. :P )

There are usually four large sales a year.

The big ones are Winter (December) and Summer (June), where most of the catalogue is discounted over a period of a couple of weeks, often including bundle sale and flash sales. These tend to also have the best discounts.

The Spring (March-April) and Fall (September-November) tend to be smaller (part of the catalogue discounted) and employing some special scheme (e.g. insomnia sale, mystery sale).

Additionally, there are, of course, the weekly sales, Monday and Friday (occasionally Thursday).

Finally, there might be limited surprise sales at unknown times (either on launch or for no special reason).

And since you got your answers already, let me say how much I like your avatar picture! ;)

They're waiting for you Gordon...in the test chamber.

Still better than pu-ing right on it.

"Unforeseen Consequences"

This is still my favourite two words in any PC game ever made. And all hell broke loose after that.. :)