When Sony was invested in designing and planning its next-generation console, it hoped to have a much better start than it did with the PS3. While its expectations were high, nothing could prepare it for the massive success that would follow.
Sony has announced that the PS4 has sold through 35.9 million units worldwide as of January 3rd, 2016. Since it's just over two years into its lifespan, this equates to over 17 million units sold per year, which is PS2 territory. Though, it's worth noting that in 2015 it outsold the previous year by a full 1.5 million, so it's actually increasing over time as it builds a library and reduces in price.
The PS4's high volume of sales now makes it the eighth best-selling console of all-time, now behind the 49.1 million of the Super NES.
It is forecasted that it'll sell over 50 million total units by the end of 2016, putting it on pace to surpass the PS3 and Xbox 360, which stand at around 84 million units sold, by the end of 2017. How well it'll perform in its later years will depend upon how consumers react to the introduction of its first wave of high-profile AAA exclusives, and the reduction of its price point beyond $299.
The PS4 has led the generation in sales for several reasons, including Sony's thoughtful positioning of the device. While the Wii U has struggled to build a name for itself, and Microsoft has had to fumble around with its marketing of the Xbox One, Sony has stuck to its "gaming-first, support games and developers" mantra from the moment the device was announced. This, in addition to its strong reputation as a leader in home game consoles, has propelled it into a position where it leads in market share by a significant margin just two years into the generation.