Any benefit to convert a traditional IRA to ROTH for 80 yo with 1M$ balance?

If you convert to a Roth, you pay income tax on the ENTIRE balance this year. The primary benefit to converting is that there is not tax on FUTURE earnings in the account. At age 80, it is significantly less likely those earnings will be sufficient to make up for the immediate taxes.

If you were 20 or 30, I would say make the conversion. At 80, you are probably just as well off keeping the plan you have.

You got the standard myopic answers here so far - - - - but there is a BIG benefit to converting the trad to a Roth for your heirs. A conversion now will eliminate the requirement for them to take required minimum distributions on your inherited Roth.

There will be a doozy of a tax bill.

Only that you'd pay the tax instead of your heirs.

I can't think of a financial reason to convert the whole thing. The effect would be the same as if you had $1M of income for the year, just due to that. I guess there might be some corner cases, such as if you were planning to donate more than $1M of non-IRA stuff in that year, anyway.

For someone younger (say, 55 and retired), it might be an advantage to convert a small amount of the traditional IRA to Roth. That would be the case where the retiree has little to no income, and is living off substantial non-retirement savings. The extra income would keep them out of Medicaid territory, but still allow them to purchase ACA insurance at very good rates. That worked for us a few years back, but we were in an ACA-friendly state (California). An 80 year old is presumably on Medicare, or something comparable.

Doing a partial conversion could also offset a smaller donation to charity that was going to be made anyway, if the person does not have enough income to deduct from.

Only if you want to write a check for a few hundred thousand to the government for taxes. And let's not forget the state.

Otoh the government needs the money. They were born to spend.

probably not, as all taxes on the balance of the account would have to be paid at conversion. Better to just withdraw at least the annual minimum and pay the taxes on reportable gains each year.