Instant Interest version 26.3.0.0 has been released.
12 rate changes were observed for the 3rd quarter.
Federal:
Underpayment rate changed to: 7%
Overpayment rate changed to: 6%
Ref: https://www.irs.gov/payments/quarterly-interest-rates
Alabama:
Underpayment rate changed to: 7%
Ref: Quarterly Interest Rates – Alabama Department of Revenue
Arizona:
Underpayment and overpayment rate changed to: 7%
Ref: Interest Rates | Arizona Department of Revenue
Massachusetts (2 updates):
2nd quarter rates: 7% for underpayment and 5% for overpayment
3rd quarter rates: 8% for underpayment and 6% for overpayment
(The 2nd quarter rates were not observed on their website at the time of rate investigation for the 2nd quarter update)
Reference: TIR 26-3: Interest Rate On Overpayments And Underpayments | Mass.gov
Michigan:
For the 3rd and 4th quarter: underpayment and overpayment are now 7.85%
Reference: Revenue Administrative Bulletin 2026-5
New Mexico:
July 1, 2026 – September 30, 2026: 7% for both
Ref: https://www.tax.newmexico.gov/all-nm-taxes/penalty-interest-rates/
NY City:
Underpayments: July 1, 2026 through September 30, 2026 is 11%
Overpayments: July 1, 2026 through September 30, 2026 is 6%
Ref: july-2026.pdf
NY State:
Period: 7/01/2026–9/30/2026: underpayments: 11% , overpayments: 6%
Ref: Interest rates: 7/1/2026–9/30/2026
South Carolina:
07/01/26 – 09/30/26: 7% for underpayment, 4% for overpayment
Ref: SC Information Letter #26-15
Tennessee:
3rd quarter changed (change is for a whole year):
07/01/26 – 06/30/2027: 10.75% on underpayment and overpayment
Ref: Tax Rates and Interest Rate
Virginia:
Underpayment and overpayment changed to 9%.