I'm going to best you and say 2.3 Million, including digital.

Between 1.5 and 2 million physical copies.

over 9000?
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I'm sorry.

Pokemon tends to have huge opening weeks in Japan. Considering this will be a simultaneous worldwide release, I'm thinking no less than 2m. There seems to be a lot of hype behind X and Y as well. I know I'll account for 2 of those 2m, since I've already got two copies preordered and paid for.

Okay, guys, stop being so optimistic. Now, even if it performs very well, we're all going to be disappointed because you expected over 2m. The hype is not unusually strong for this one, it's coming much sooner than usual (so there's saturation), 3DS has been erratic for relative sales of established franchises, the physical sales will be artificially reduced by digital buyers and XY has nowhere near the userbase BW had to sell to. There's plenty of things holding this back.

At best, I'm hoping this can match DP in its opening week.

I can't see Pokemon X/Y getting over 20 Million sold. Maybe 18+.

Pokemon has continually become more and more front loaded as time has gone on:

1,273,279~Ruby/Sapphire
1,646,064~Diamond/Pearl
2,609,126~Black/White

Pokemon X and Y will do better than Pokemon Diamond and Pearl FW, that's for sure. Going as low as to say that it'll only match that? That's quite odd. Anything below 1.8 Million will be a surprise. Anything about 2.3 Million would be unbelievable, and won't happen.

doesn't matter about user base cuz look at gen 3. Sold almost 16mil on a system that sold almost half of the DS! 2mil is not out of reach. It can possibly do more

Between 2 million and 2.3 million

That's very selective data to use considering that RS was a huge tumble from GS. Regardless, DP being higher than RS is not evidence of being frontloaded at all; although it wasn't quite in the same proportion, for LT sales, DP outsold RS considerably, too. The DS simply had a notably higher base to sell to, which allowed DP to perform better on the whole. Not gonna happen for XY.

As for BW, that's uncontestably an outlier. It was the first second generation on the same console and it had an enormous userbase to sell to. None of this applies to XY.

Also, we've seen certain major DS franchises decline considerably on the 3DS. Nintendogs, Brain Age, Layton, 2D Mario... While Pokemon is much more proven than these, it's quite possible it will lose the extra fans it got during the DS days and decline to perform closer to what RS did.