January 2019 is the 60th month of the PlayStation 4 being on sale in Japan. The gap grew in favor of the PlayStation 4 by 99,677 units in the last month and in favor of the PlayStation 4 by 97,144 units in the last 12 months. The PlayStation 4 currently leads by just 540,135 units.
The PlayStation 3 launched in November 2006, while the PlayStation 4 launched in February 2014. The PlayStation 4 has sold 7.79 million units, while its predecessor the PlayStation 3 sold 7.25 million units.
source: gamezpot.com