The rule is not 90% of the previous year. It's 90% of the current year or 100% of the previous year.
2024 Form OR-10 instructions:
"Required annual payment: The total amount of all tax payments, including estimated tax and withholding, that you must make in order to avoid being charged underpayment interest. Your required annual payment is the lesser of:
• Ninety percent (90%) of the tax after all credits shown on your 2024 Oregon return; or
• One hundred percent (100%) of the tax after all credits shown on your 2023 Oregon return (also known as “safe harbor”)."
