If you’re the kind of saver that’s on target for an early retirement thru high retirement savings then you should have a pretty good idea of what your annual expenses are. Throw in a buffer + known liabilities (roof needs replacing, aging car, health issues, etc).

There’s a few methods here - and it’s going to depend on your mix of retirement accounts (ROTH vs Trad vs HSA vs non-tax advantaged). There’s lots of tools to help plan scenarios - I particularly like ProjectionLab. I would also recommend hiring a professional that can assist in the planning and especially taxes during early retirement.

For SEPP 72T you need to make similar withdrawals every year for at least 5 years or until you hit 59.5 of age. My plan is a mix of SEPP 72T + non-tax advantaged accounts for 5 years. During those 5 years I will also be making ROTH conversions from my Trad accounts. Once the 5 years are up - I will continue my ROTH conversions but can finally start withdrawing the money I converted 5 years ago (this is a ROTH conversion ladder).

I was a bit of a late bloomer and spent my 20s working my way into tech - so I won’t retire at 45 - but am on target for 50ish.