An extension to file is not an extension to pay tax.
The City of Portland and Multnomah County jointly administer a Combined Business Tax (covering the Portland Business License Tax and the Multnomah County Business Income Tax) through the Revenue Division. Filing a federal extension does not by itself extend the local filing deadline - a taxpayer must file Form EXT and attach a copy of the federal extension, checking the "Extension Filed" box on the return when it is eventually filed. Doing so grants a 6-month extension to file, generally to October 15 for calendar-year filers. The tradeoff is a payment safe harbor: at least 90% of the current year's tax or 100% of the prior year's tax must be paid by the original due date to avoid underpayment penalties.
| Item | Detail |
|---|---|
| Form required | Form EXT, with a copy of the federal extension attached |
| Extension length | 6 months, generally to October 15 for calendar-year filers |
| Payment safe harbor | At least 90% of current-year tax or 100% of prior-year tax paid by the original due date |
| Authority | City of Portland / Multnomah County Revenue Division, Combined Business Tax extension guidance (Form EXT) |