I've collected examples of PS3 & 360 sales in each year, showing (Sep-Dec) / (Jan-Aug) sales.  We can then estimate 2004 Sep-Dec sales range by applying similar ratios.

[PS4]

2007: 4586k / 3335k = 1.4
2008: 4750k / 5708k = 0.8 <- Price cut effect & MGS4 boosted fist half of year
2009: 8894k / 4328k = 2.1 <- PS3 Slim in September
2010: 7043k / 6338k = 1.1
2011: 7734k / 6579k = 1.2

[360]

2006: 3687k / 3125k = 1.2
2007: 4823k / 3087k = 1.6 <- Price cut in August, Halo 3 in Sep.
2008: 6847k / 3855k = 1.8 <- Price cut in September
2009: 5810k / 4555k = 1.3
2010: 7911k / 5624k = 1.4

PS4 Jan-Aug 6.0M (my estimate)
XB1 Jan-Aug 2.3M (my estimate)

PS4 schedule until Dec is good but no price cuts, so I'm going to give it a conservative 1.2 ratio, meaning 7.2M units sold in Sep-Dec period, so my estimate is PS4 could reach 17.4 Million units by end of 2014.

XB1 has had an early price cut, and players are excited for upcoming games, however it already had it's biggest game of the year Titanfall. I'm going to give it a more generous ratio of 1.5, meaning 3.5M units sold in Sep-Dec period, so my estimate is XB1 could reach 8.8 Million units by end of 2014.

If I had to give ranges I'd say PS4 16.8M~19.8M and XB1 8.0M~9.0M.

What say you?

Xbox One releasing in more countries will help. Xbox One was also more expensive for the first half of the year Xbox One will easily pass 10 million this year.

FWIW using similar reasons I gave Wii U a 1.9 boost, so I think Wii U will end the year around 10.4M.

It's true launching in more regions is a bit of a wild card.

As for the price, it's already been in effect since June, and is not a real price cut since it involved dropping kinect so I don't think the boost will be as high as that.

Price cut will have the biggest effect during the holidays. Especially when games are bundled with the system.

I think that's too high. If/when the price cut has any effect on the holiday sales, I think it could get to 9 million at the most.

I'm thinking a lot of people will be surprised by the holiday numbers.

Surprised at how low they are?

Anything, really. I don't think anyone on here can accurately predict what will happen these holidays. Anything could happen.

For that matter, kind of wonder if we're even going to really KNOW for certain what they both sell during the holiday period; VGChartz seeeems to have some holes in terms of keeping track, even with adjustments. Microsoft hasn't really raised a peep about its sales figures in... a fairly long while... and Sony might start sticking to the trend of just announcing big milestones, like 5 or 10 million marks. NPDs are only going to show a piece of the picture- and, for that matter, the piece is going to illuminate the Xbox One more favorably than it'll be performing in the wider world, given the U.S. is its strongest market- so, yeah. o.o Think both companies will announce holiday sales? I know they did last year, but I have no idea if it's a trend during the last gen too.