Thanks to you and @SteamTrain for the comments.
I missed the fact that the oregon.gov website specifies the 90% level applies to the current tax year and you must pay 100% of the previous tax year to avoid penalty.
Interestingly, I paid about 92% of the previous year (2023) tax liability, but my tax liability for the current year (2024) was much higher and I paid way less than 90%. Despite that, I received a letter from the Oregon Department of Revenue saying I did not owe the penalty that TurboTax calculated for underpayment.
Who knows what that means, since I did not meet their stated requirements.
FYI, I paid one estimated tax payment in April, 2024, then had tax withheld from IRA distributions. I did a single IRA distribution in December, 2024, so there was one payment to Oregon Department of Revenue which occurred in the last week of December.
When calculating that I did not owe a penalty, the Oregon Department of Revenue split the amount of tax withheld from my IRA distribution in to four equal payments occurring on the normal due dates for quarterly estimated taxes. To clarify, if I had paid $1000 in Oregon tax withheld from my IRA distribution in December, Oregon treated it as four payments of $250, paid on April 15, 2024; June 17, 2024; Sept 16, 2024 and Jan 15, 2025.
On the worksheet for this, TurboTax also spread out the withholding amount. However, the TurboTax calculation results in me owing an interest penalty for underpayment. Oregon Department of Revenue didn't show me a worksheet in their letter, but does show the credit amounts and dates they used. Oregon's amounts and dates are the same as the TurboTax amounts and dates. But Oregon says I own nothing.
After looking at all this and with the help of your comments, I think TurboTax followed the rules correctly, but got a different answer than the Oregon Department of Revenue. In this case, since the Oregon Department of Revenue is sending me a refund of the penalty I paid based on the TurboTax calculation, I think I'll go with Oregon's take on this!!
