Mass. Gen. Laws ch. 59 § 57
Except as otherwise provided, bills for real estate and personal property taxes shall be sent out seasonably upon commitment in every city, town and district in which the same are assessed, and shall be due and payable on July first of each year for all purposes except the calculation of interest as provided in this section. If any betterment assessment or apportionment thereof, water rate, annual sewer use charge and any other charge added to such tax, or more than one-half of the balance of any such tax as reduced by any abatement, remains unpaid either after November 1 of the fiscal year in which it is payable, or after the thirtieth day after the date on which the bill for such tax was mailed after October 1, interest at the rate of 14 per cent per annum, computed from the due date, shall be paid on so much of the unpaid amount as is in excess of said one-half of such balance. If the whole or any part of such tax remains unpaid after May 1 of such fiscal year, in addition to the interest as aforesaid, interest at such rate shall be paid on so much of the balance of such tax not so paid as does not exceed one half of such tax as reduced by any abatement and computed from May 1 of such fiscal year. On or before April 1 of such fiscal year a notice shall be sent out showing the amount of such tax which, if not paid by May 1, shall bear interest computed from May 1. Bills for taxes assessed under section 75 or section 76 shall be sent out seasonably upon commitment, and shall be due and payable on the thirtieth day after the date on which the bill for such tax was mailed for all purposes except the calculation of interest as provided in this section. Taxes shall bear interest as hereinbefore provided in this section with respect to real estate and personal property taxes generally; provided, however, that if a bill for any such taxes is mailed on or after April 1 of the fiscal year to which the tax relates and remains unpaid after the thirtieth day after the date on which such bill was mailed, interest at the aforesaid rate, computed from the due date, shall be paid on so much of the tax that remains unpaid. In all cases where interest is payable it shall be added to and become a part of the tax. Interest which pursuant to this section shall have been added to and become a part of any tax other than a tax reassessed under section seventy-seven shall be waived by the collector if the amount of such tax, exclusive of such interest, is tendered to him within thirty days after the bill for such tax is first sent. A first actual real estate tax bill sent out for fiscal year 2008 or any subsequent year pursuant to this section shall contain a statement that there exists a delinquency if any tax, betterment assessment or apportionment thereof, water rate, annual sewer use, or other charge which may constitute a lien is overdue for more than 90 days. Such delinquencies shall not include amounts due relating to fire service, electric, water or sewer use in any city or town served by more than 1 independent municipal or district fire, electric, water, sewer, or joint water and sewer district or in any city or town served by an independent municipal or district fire, electric, water, sewer, or joint water and sewer district that is not principally domiciled in that city or town.
Notwithstanding the first paragraph, if the last day for making a tax payment without incurring interest on a bill for real estate or personal property taxes occurs on a Saturday, Sunday or legal holiday, or on a day on which a municipal office is closed as authorized by charter, by-law, ordinance or otherwise for a weather-related or public safety emergency, the payment may be made on the next day on which a municipal office is open, without penalty or interest.
For the purposes of determining jurisdictional interest requirements on appeals brought pursuant to chapter 59, the date of delivery for a payment for taxes pursuant to this section that is, after the period or date prescribed by this section, delivered by United States mail or by an alternative private delivery service to the collector shall be deemed to be the date of the United States postmark, the date of the certification of mailing stamped and postmarked by the United States Postal Service, the date of a certified mail receipt provided by the United States Postal Service or other substantiating date mark permitted by the rules of practice and procedure of the appellate tax board that is affixed on the envelope or other appropriate wrapper in which the payment is mailed or delivered if the payment was mailed in the United States in an envelope of such appropriate wrapper, first class postage prepaid, or delivered to an alternative private delivery service, properly addressed to the collector; provided, however, that a taxpayer shall have the burden of proving the timely mailing of any payment of taxes to said collector pursuant to this section and the collector shall have no obligation to maintain any record relative to the date of mailing of the tax; and provided further, that nothing in this section shall be construed to place the burden of proving any untimely mailing on the collector. As used in this section, "United States postmark" shall mean only a postmark made by the United States Postal Service. This paragraph shall not apply to the calculation of interest pursuant to the first paragraph of this section.
Mass. Gen. Laws ch. 59, § 57