I got The Witcher 3 with my graphics card and it was for GOG and I've been playing it for a while and i would like to get the DLC. The problem is that i have £20 on my steam account with nothing to spend it on, so I was wondering if i could buy the expansion pass and when the DLC comes out I could download it and use it with the witcher 3 from GOG. Do you think this would work?

but if you owns the main game in STEAM but the DLC in GOG? it can work? becouse that is my issue....

It might work, but probably won't Oh yes, you're quite correct, that's a thing Steam does now.

Thanks for your replies, looks like ill wait till i can get it on GOG

EDIT: nevermind, I misread :S
Thought you wanted to use GOG DLC with Steam base game, not the opposite :D
The Witcher 3 is DRM free on Steam, but sadly Steam doesn't allow you to install DLCs without the base game (1 point for GOG!)

Actually, GOG prevented you from purchasing DLC without the base game - that might have changed since the last time I checked. At any rate, I would not be so certain about GOG DLC installer working with the Steam's version of the game - they are designed for the DVD version primarily. If the installer even picks up the Steam installation properly, as soon as CD Project releases a patch, it'll probably break the installation as Steam is unaware of that DLC, it would most likely treat is as a mod.

I tried and I can get to the checkout page with just 1 DLC from divinity: original sin (I don't own the base game). Seems it doesn't charge me for the base game. I didn't go through the purchase of course.

I'm not sure about it because people say that you can play the Steam version without Steam running at all, so maybe it works if you change the location of the installation folder in order to get the DLC recognize it. I can't tell if it works, but this was not the matter anyway :)

Oh no, install location shouldn't matter at all - you can launch a lot of Steam's games without Steam running, in fact there's a very handy list of games we know are DRM-free on Steam (it even includes Half-Life 2 and its expansions, funnily enough - yes, you can run them without having Steam running, or even having Steam installed on your system at all.)

Anyway, my point is that even in spite of being DRM-free, the DLC installer might be able to differenciate Witcher 3 installed from DVD, GOG installer and Steam - I have noticed that at least games insalled via Galaxy create GOG-specific files in the games directory which are not used by the game itself at all.

Oh I see, still we're able to download the Galaxy-independent installation files. It likely won't work, like you said. The risk of wasting money is high, until someone provides a feedback.

There's actually an option, you go into this official website and you can trade directly a gog version for a steam or origin version just ONCE. thewitcher. com/en/exchange

What if i already have witcher 3 and hearts of stone dlc and i only want to get blood and wine dlc from steam ? can i transfer over my gog witcher 3 + hearts of stone for steam version?

No. Gog.com is a sister company to the developers of TW3, that's why you can exchange Steam for GOG, but Steam will not (can not) do the same. If you want Blood and Wine from Steam, get it here.