We retired at 58.

We spoke to a couple of advisors that we met through dinners they held.
One said "You don't need me, you are doing fine."
The other said, "Yes, you can afford to retire."

I did figures on the back of an envelope one lazy Saturday afternoon while she was taking a nap.

Figured what our usable income that we were living on was. Paycheck minus taxes minus FICA minus company health insurance minus 401K & IRA contributions PLUS what post-retirement, pre-medicare company health insurance would cost. The things that will all drop off when I quit, plus the one that will be added.

Then compared that with 4% of our total investment & retirement portfolio.
Realizing that you can take 401K at 55, and IRA at 59 1/2, and SS at 62. And company pension at any time.

If the 2nd number is more than the 1st number, you are gold.
We were, so I told my boss that if there was a layoff coming, I volunteer.

Do NOT NOT NOT retire on a shoestring. Make sure the 2nd number is comfortably higher than the 1st.
OTOH, you don't want to expire at your desk waiting for One More Year.

Switching from savings mode to spending mode can be mentally difficult.

Our income tax was surprisingly low the first few years. Went up later, though.