Some tax jurisdictions have special rules beyond normal interest calculations which affect the calculation of interest on overpayments and/or underpayments. In some cases Instant Interest prompts you for additional information needed to calculate the interest schedule. The following situations have special handling which either requires additional input or calculates interest in an unusual manner:

Federal – Tax-motivated underpayments

California, Federal, and Virginia – Large underpayments ("Hot interest")

Federal, Alabama, Arizona, and Virginia – Large corporate overpayments

Alaska – Oil and gas production

Colorado – Discount for early payment

Delaware – Delayed interest accrual on refunds

Florida, New York City and Utah – Interest rate fixed based on Due Date

Iowa – Rounded monthly rate

Missouri – Refunds for amended returns

New Jersey – Lower interest on extensions granted or discretionary reductions

Oregon – Additional 4% for Delinquencies after 60 Days

Tennessee – Interest rate fixed based on Assessment Date

Texas – 60 day grace period

Option to apply payments to interest or principal

52-53 Week Taxpayer