Also be aware that you can only move the inherited IRA to a beneficiary IRA by nonreportable trustee-to-trustee transfer, not by distribution and rollover. Once you receive a distribution from the IRA it cannot be rolled over to continue to defer taxation.
Money in this traditional IRA is generally deferred income on which your grandmother had not yet paid taxes, so you as beneficiary are responsible for paying the taxes when distributed.
$88k (28.1%) federal tax plus $23k (7.4%) state tax on $313k of income is a combined marginal tax rate of about 35.5%, not 50%.
It seems likely that your income presently falls in the 22% federal tax bracket and that you might be able to incur another $70k or so before reaching the 24% tax bracket. Taking all of it in one year would likely push some of it into the 32% tax bracket. You can verify that more precisely by entering an incremental amount of IRA income, say $1,000, and seeing how much your tax liability increases. An increase of $220 in federal tax liability for a $1,000 increase would indicate that you have a 22% marginal federal tax rate on this portion of your income.
Note that in 2026 the tax rates are scheduled to revert to the levels that were in effect before the Tax Cuts and Jobs Act of 2017 temporarily lowered them, so the 22% bracket will go back to being a 25% tax bracket. This suggests that it may be beneficial to take roughly equal amounts over the 4 years 2022 through 2025 for these amounts to be federally taxed at less than 25%, mostly at 22%. Of course you'll also want to take into account your state marginal tax rate on these distributions, likely making the combined marginal tax rate about 29% if taken in equal portions over the 4 years prior to 2026. This would save you about $20k in federal taxes over receiving the entire $313k in a single year, about the best you can do.
