“Does it really matter which account I spend first?”

Yes. On a seven-figure portfolio it's routinely a six-figure decision, it's entirely free to get right, and essentially no free calculator models it.

The three buckets are not the same money

Retirees typically hold three kinds of account, and they behave completely differently:

• Traditional IRA / 401(k). Every dollar out is ordinary income, taxed at your top rate. The IRS owns a slice and is waiting.
• Taxable brokerage. Only the gain is taxed, at capital-gains rates, which can be 0% in the right bracket. Your basis comes out free.
• Roth. Already taxed. Grows tax-free, comes out tax-free, and has no RMD in your lifetime. It's the only bucket the IRS can never touch again.

The conventional advice, and why it's not obviously right

The standard rule is: spend taxable first, then pre-tax, then Roth — let the tax-advantaged accounts compound as long as possible.

It's reasonable, and it's often wrong. Letting the IRA compound also grows the RMD. Drain the taxable account through your sixties and you arrive at 75 with a bigger pre-tax balance, a bigger forced withdrawal, a higher bracket, and possibly an IRMAA surcharge — having "saved" tax you'll now pay at a worse rate with no flexibility left.

Sometimes the better move is the opposite: deliberately draw the IRA down early, at low brackets, before the government starts choosing for you.

Spending the Roth first is almost always the mistake

It feels good — no tax bill. But you're spending the only asset with no future tax liability and no RMD, while leaving the IRS's claim to compound. It's the one order that's consistently wrong.