Mass. Gen. Laws ch. 79 § 37
Damages under this chapter shall bear interest at the rate calculated pursuant to the provisions of this section from the date on which the right to damages under this chapter vested until paid, except that an award shall not bear interest after it is payable unless the body politic or corporate liable therefor fails upon demand to pay the same to the person entitled thereto. Interest shall be added by the clerk of the court to the damages expressed in a verdict, finding, or order for judgment. A judgment, whether against the commonwealth or any other body politic or corporate, shall bear interest at the rate calculated pursuant to the provisions of this section from the date of the entry of such judgment to and including the last day of the month prior to the month in which such judgment is satisfied, except that a judgment against the commonwealth shall not bear interest if it is satisfied within thirty days of such entry.
Where the period for which prejudgment interest is owed is not more than one year, such interest shall be calculated at an annual rate equal to the weekly average one-year constant maturity treasury yield, as published by the Board of Governors of the Federal Reserve System, for the calendar week preceding the date on which the right to damages under this chapter vested. Where the period for which prejudgment interest is owed is more than one year, such interest for the first year shall be calculated in accordance with the preceding sentence, and such interest for each additional year shall be calculated on the principal amount due at an annual rate equal to the weekly average one-year constant maturity treasury yield, as published by the board of governors of the Federal Reserve System, for the calendar week preceding the beginning of each additional year. Post-judgment interest shall be calculated in the same manner as pre-judgment interest, but using, in the first year after judgment, the rate for the calendar week preceding the date on which judgment entered, and in any additional year, the rate for the calendar week preceding the beginning of such additional year.
The secretary of administration and finance shall maintain a schedule of the rates described herein for distribution, upon request, to all clerks of courts and all board of officers upon whom authority to take real estate by eminent domain under this chapter on behalf of any body politic or corporate that has been conferred by law.
Mass. Gen. Laws ch. 79, § 37