this is a million dollar question that I've had an extremely difficult time unpacking.
Conventional wisdom says the 80%... but a lot of my money goes into kids I won't be supporting any further (i hope at least), saving for retirement (there's 20% right there), a mortgage I'm not going to have (another 20%), life insurance I won't have to pay, disability insurance I won't have to pay anymore, etc.
In fact currently probably 70% of my current expenditures aren't something I should have to worry about.
Now, as someone who wants to retire before SS and medicare, I know that those expenses are going to be big for me in those first few years of retirement... and the entire point of retiring early is to be able to spend some pretty big money on traveling, activities, etc.. the stuff you never have time for when you work and raise a family... so there's a massive uptick in consumerist spending.... so maybe that all levels out.
On the other side of the coin, you'd have to be pretty confident in yourself that you are going to need a bunch of money post 80-85 when deep airline travel probably wouldn't be something fun, you probably are slowing down, and there's no stigma to eating at early bird special times..... I've seen this with my grandfather.. post 80 his expenditures have just fallen off big time compared to his 62-75 time frame where he really did a lot of stuff.
I think as always the best plan is to over-save because it's sure easy to worry about "too much money" at a later date in life.... so i'm going with 70%