As Kenaces pointed out, someone drawing 25K/yr from a portfolio will barely crack into the 15% tax bracket. Most of your withdrawals will be tax free or very low tax.

+1

In round numbers, assuming $18K/yr goes into a 401k, $5500/yr into a Roth IRA, and $51,500/yr into a taxable account*, when the total stash reaches $625K there will be

$425K in taxable

$150K in traditional

$50K in Roth

*Requires gross income ~$131,700 for a single person with no state tax and $25K/yr non-tax expenses.

Drawing proportionally from each of those (doable without penalty if one is 59.5 or older) to fund $25K spending the federal income tax is $0 because the amount coming from traditional accounts is less than 1 standard deduction and personal exemption.

Or, one could convert $10,400/yr from traditional to Roth for $0 tax and withdraw $25K from traditional, also for $0 tax even with a $0 basis, as long as all the gains are long term.

For those with annual spending higher than $25K, taxes will become an issue at some point, but for a one line equation the the simple math isn't too bad.