Effective January 1, 1994, the state of Oregon adds 1/3 of 1% to the monthly rate (or 4% annually) for delinquencies not paid within 60 days of assessment.

When an underpayment is calculated for a due date after January 1, 1994, the following prompt is displayed:

Instant Interest calculates 60 days after the date entered. If the deficiency is paid not off by that date, Instant Interest increases the interest rate used by 4 points.