Biggest Tax Mistakes Oregon Filers Make (2026)

Figures are for tax year 2025 (returns filed in 2026) unless marked as tax year 2026 (returns filed in 2027). Each item names the official rule behind it; the sources are listed at the end.

1. Treating an extension as more time to pay

The most common expensive mistake on this list. An extension gives you until October to file, not to pay, and Oregon does not allow an extension of time to pay even when the IRS does. Tax unpaid after the April due date can draw Oregon’s 5 percent failure-to-pay penalty plus interest, at an annual rate of 8 percent for 2026. Federally, the failure-to-pay penalty is 0.5 percent of the unpaid tax per month, up to 25 percent. Paying an estimate of the balance with the extension request limits both.

2. Not filing because you cannot pay

Filing late costs more than paying late. Oregon adds a 20 percent penalty when a return is filed more than three months after its due date, including extensions, so a late, unpaid return can reach 25 percent in penalties before interest. Three consecutive years unfiled brings a 100 percent penalty on each year’s unpaid tax. The IRS failure-to-file penalty is 5 percent of the unpaid tax per month, up to 25 percent. Filing on time and arranging a payment plan usually costs less.

3. Skipping the Oregon return that carries the kicker

The kicker is a credit on the Oregon return, not a check in the mail. For tax year 2025 it is 9.863 percent of your 2024 Oregon tax liability, and DOR requires a filed 2025 Oregon return to claim it, even if you do not otherwise have to file, along with a filed 2024 return that showed a liability. This is the mistake that catches people whose income dropped in 2025 after a taxable 2024: no filing requirement, but a kicker waiting on a return. See the Oregon kicker, explained.

4. Leaving refundable Oregon credits on the table

Several Oregon credits are refundable, which means they can pay out even when no tax is owed, but only on a filed return:

• Oregon earned income credit: 9 percent of the federal EITC, or 12 percent if the youngest dependent was under 3. ITIN households may qualify through Schedule OR-EIC-ITIN.
• Oregon Kids Credit: up to $1,050 per dependent age five or younger for 2025, phased out between $26,550 and $31,550 of qualifying income.
• Working family household and dependent care credit: for working families who paid for dependent care, with proof of payment to the provider.

The full list, with the 529 and ABLE credits, is in the best Oregon tax deductions and credits.

5. Fixing an estimate shortfall in December

Oregon charges underpayment interest when tax after credits and withholding is $1,000 or more and payments fell short of 90 percent of this year’s tax or 100 percent of last year’s. The interest is figured on each installment separately, so a large payment in December does not undo a missed April or June installment. DOR’s own advice is to pay a shortfall as soon as you spot it. Federally, the prior-year safe harbor rises to 110 percent when prior-year AGI was over $150,000 ($75,000 married filing separately). See quarterly estimates.

6. Letting a refund year expire

Oregon refunds withholding and estimated payments only on an original return filed within three years of its due date, not counting extensions. After that, the money cannot be refunded or applied to another year. The IRS has its own three-year limit. Unfiled 2023 returns reach that line on 15 April 2027. The back taxes service covers catching up on unfiled years.

7. Using credited 529 money for K-12 tuition

Federal law lets 529 money pay K-12 tuition. Oregon does not follow that rule. Funds in Embark or the MFS 529 Savings Plan are for higher education expenses, and if an Oregon credit or subtraction was based on contributions later withdrawn for K-12 tuition, the Oregon return may need an addition or a credit recapture.

8. Assuming no 1099 means no income

Payment apps and marketplaces only have to send a Form 1099-K when payments exceed $20,000 and 200 transactions, and businesses only issue a 1099-NEC for 2026 payments of $2,000 or more. The IRS is clear that income below those lines is still taxable and still reportable. The reverse mistake happens on the payer side: small businesses still sending 1099-NECs at the old, lower line create paperwork they no longer need to, and ones that stopped entirely miss contractors paid $2,000 or more.

9. Copying the federal return onto the Oregon one

The Oregon return starts from federal adjusted gross income but departs from the federal return in ways that change the answer:

• The federal tax subtraction is capped at $8,500 for 2025 ($4,250 married filing separately) and phases out with income.
• Oregon is disconnected from the federal qualified business income deduction (Section 199A).
• Oregon’s standard deduction is far smaller than the federal one ($2,835 single, $5,670 joint for 2025), and Oregon itemized deductions come from Schedule OR-A, which can differ from the federal figure.
• Oregon does not tax Social Security benefits, and taxes nonresidents on income from Oregon sources, which matters for anyone who lives in Washington and works in Oregon. See multi-state returns.

10. Deductions built on reconstructed records

DOR states that estimates or approximations do not qualify as proof. A mileage log written up in April, or a stack of receipts with no note of the business purpose, is where deductions are lost in an audit. The fixes are habits, covered in the best ways to organize tax documents.

11. Forgetting the Portland-area local taxes

Residents inside the boundaries may also owe the Portland Arts Tax, Metro’s Supportive Housing Services tax and Multnomah County’s Preschool for All tax, all due on the April date and administered by the City of Portland’s Revenue Division. They are filed separately from the Oregon return, so they are easy to miss. The tax deadline calendar lists them with the other April dates.