I was looking at the totals and it currently trails gameboy by about 17 million.  

With PS5 having BC will it’s price severely effect the long term ps4 sales?  For instance if ps4 is only $150 cheaper than PS5 at launch would more people just save and have the ability to play all the games?  Alternatively PS5 could come in at $500 or ps4 could get a permanent drop to $200 or both which would obviously make it a far bigger leap to get to the next gen and probably drive more sales to the ps4.

Now all of that could be irrelevant as PS4 will still sell a few million this year with the holidays coming up and it probably being fairly cheap in some bundles (there were $200 ones last year) and then it’ll have the whole year until November (though I wish to god they would release in September or October and get that initial sales boom out of the way BEFORE the holidays and get a 4 month sold out window rather than just 2) to sell with PS5 only stealing mindshare.

i think it’ll pass the gameboy sometime in early 2021 (I’ll say Q2) personally as the sales are declining anyway and ps3 took quite the plummet after ps4 was announced even with the lack of BC.  So I think it’ll need this holiday and next and then probably about 4 more months to pass the GB but I do think it’ll continue a decent deal afterwards with it being made from less custom parts and being able to sell in developing nations for years to come as those parts come down in price 

19 of March 2021

How very specific 

I think the PS4 will overtake the GB in Q1, 2020... but lets not forget it first has to best the PS one which I hope will be done by year end.

I think either Calander Q4 2020 or Q1 2021.

They are at 100M shipped as of Calander Q2 2019, and they shipped 3.9M in Q3 2018 and 8.1M in Q4. I could see this year falling to 2.5M and 5M putting them at around 107 - 108M by the end of 2019. They should be able to move another 10 - 12M units next year putting them around 118 - 120M by Q4 2020. If they don't hit 118.69 by Q4 2020, they will far surpass it in Q1 2021.

As for when it will pass it on VGChartz. I'd go with April 2021.

I don't think there is any doubt it will surpass 120M sales at this point. Then again, I don't think it is as far fetched as some people believe, to see it come close to matching PS2. A MSRP of $199.99, a new Slim Model, and $149.99 Holiday deals, and it can very easily continue selling for quite a few more years. With X86/Radeon in both PS4/XBO and PS5/XB4, this is going to be the easiest previous console generation to continue supporting in the histoyr of console gaming. That will mean software for a long time to come.

Well, 120m seems almost a given. It remains to be seen how much it goes beyond that.

Both the PS1 and the PS2 sold a lot after their successors released (30 and 50 million respectively I believe?). So, it's not unfeasible the PS4 moves a significant amount of units in the early 2020s, although it'll partly hang on another pricecut.