When does interest accrue on unpaid bills?

Excise tax is due and payable 30 days from the date of issue.  If you are unable to pay your tax bill, Massachusetts General Law mandates that interest at 12% be added to the amount due from the due date to the date of payment.  A tax bill is considered “paid” upon receipt by the Treasurer/Collector, not the post mark on the envelope.  Other collection fees can be added.