Amazon has around 80 million reasons to be excited for Prime Day

Tuesday is Amazon Prime Day, a sales event in which Amazon discounts a number of items for those who subscribe to its Prime membership service.

It is, in short, going to make Amazon lots of money.

Prime currently has somewhere in the ballpark of 85 million subscribers, according to recent Consumer Intelligence Research Partners estimates charted for us by Statista. That's a 22-million subscriber increase over this time last year, according to CIRP's figures. So the Prime Day buying base will be a good ways larger than it was in 2016.

It's hard to say if CIRP's figures are exact - Amazon notoriously refuses to give a specific Prime subscriber count, and other recent reports have pegged the total closer to 80 million. But all signs suggest the number is growing.

That's a good thing for Amazon. Prime users spend roughly twice as much on Amazon in a year than non-Prime shoppers, according to CIRP. Beyond that, past studies have said the vast majority of Prime members don't even bother to compare prices at other retailers before pulling a trigger on a product.

All of this goes a long way in explaining how Amazon makes hundreds of millions of dollars on a sales event promoting a somewhat mixed bag of products. Last year, for instance, buying guide site The Wirecutter scanned roughly 8,000 Prime Day deals and found only 64 to be worth buying.

Mike Nudelman/Business Insider/Statista