If we go on a conservative 80% of sales made until launch of PS5. Then it getting 111M by March it would mean 139M, and if by Nov it would get to 147M.
Even if we expect the worse legs like PS3 (don't think it will do it because price cut will be more feasible on PS4) then we get 123M and 131M.
Anyway nothing suggests below 120M at the moment.
PS4 basically has 120m on lock by now, its hard to imagine it doing any less than that in lifetime sales at this point.
Number of days to reach 50M from 40M : 198 days
Number of days to reach 60M from 50M : 187 days
Number of days to reach 70M from 60M : 175 days
Number of days to reach 80M from 70M : 227 days
Necro-bump this 2020: http://gamrconnect.vgchartz.com/thread.php?id=229249