Valve don't usually publicly announce their sales dates before hand so it's only those "in the know" who'll know for certain right now. I did however see 2 supposed leaked starting dates for both their Autumn (just gone) and Christmas sales last month, the former of which did actually turn out to be true so we can probably assume the other date is as well:
Thu 19th
They always update their deals at 6pm GMT so I'd check at that time on Thu to see!
annnd as always to those of you buying on Steam,
wait for the daily deals. Even if the game(s) you're after are part of their site-wide discount knocking off 50% or whatever, If it's not a daily deal (or a flash/community one), wait. Don't buy it just yet.
The daily/flash/community deals are the max discount you'll see for a game during the sales so always wait to see if a game becomes one of those first before you buy. If it doesn't become a daily it still might become a flash deal, or a community choice deal, both of which would offer the same % discount as a daily would. If it doesn't get any of those? Buy on the last day of the sales.
So:
Daily deal: Buy now if you want it as that's as cheap as it's going to go. If it's like previous sales they'll also give you a second chance to buy the previous days daily for the same price when the new dailies go up too. There's also a chance they'll reappear as a flash deal or a community choice deal if they have either of those running again too but that's not guaranteed.
Flash deal: Buy now, should be the same price as it would be if it was a daily.
Community Choice deal: Buy now, should be the same price as it would be if it was a daily.
Discounted but not one of the above three: Wait for the above, if it doesn't become one then buy on the last day when you can be sure it won't go any cheaper.
Most of you are probably more than familiar with that already and won't need telling but there are still a lot of people out there who don't and will just randomly buy stuff regardless, always like to say just incase. This way you save the most money and don't buy anything on sale to later see it go even cheaper and end up kicking yourself
Also as awesome as some of their deals usually are - if you see something which looks too good to be true as far as price goes, it probably is and they've made a pricing error. I haven't seen it happen very often but if it does and it's something you want, buy it!!. Got a few insanely cheap deals from pricing mistakes like this in the past (the Sleeping Dogs giveaway I did last year was from such) and they've always honoured them but they've fixed the price within a couple of minutes so you have to be fast.
It's probably a good idea to keep an eye on other digital stores too btw; GMG, GG & Amazon Digital. Steam usually dominates but last year some of these did a hell of a good job competing and offered some fantastic deals themselves, especially GMG.
