Yes.21 June.Steam sale begin.

This site https://www.whenisthenextsteamsale.com/ usually proved right.

But it showed that date for months now...

Do you want them to change the date from time to time even if that's the date when the sale begins?

No, but does seem it's based on a hunch.

Usually the info leaks from publisher's tweets or emails. They know months in advance when the sale starts.

According to SteamDB (which is a pretty reliable source of information about Steam), the next Summer Sale starts on June 21st. GOG should be a couple of weeks earlier, as usual.

Neither Steam nor GOG sales' dates have been ever confirmed. It's always business secret.

About the predictions:
- in case of Steam it is always known before, probably they have discipline issues with hundreds or thousands of publishers, some of them cannot even make games ;)
- in case of GOG it's only a guess and we can never be sure, but recently they tend to start their sale before Steam one, which is quite reasonable I think if you're competing for the same wallets.

Stay away from us you are....

Sir, I don't want to be evil any more! I want to change! Could you spare me a plus to help, sir?

Solved

Nice one:)

Don't think so. Usually there is no Weekly Sale starting before big sales. Moreover, Summer Sale tend to start in June.

It may be next week.