Section 13. Assessments made by a board of the commonwealth under this chapter shall bear interest at one rate of five per cent per annum or, at the election of the board at a rate not to exceed two per cent above the rate of interest chargeable to the body politic on behalf of which the assessment was made, for the betterment project to which the assessments relate, from the thirtieth day after assessments have been committed to the collector. All other assessments made under this chapter shall bear interest at one rate of five per cent per annum or, at the election of the city or town at a rate equal to two per cent above the rate of interest chargeable to the city or town, for the betterment project to which the assessments relate, from the thirtieth day after assessments have been committed to the collector. The assessors shall add each year to the annual tax assessed with respect to each parcel of land all assessments, constituting liens thereon, which have been committed to the collector prior to January second of such year and which have not been apportioned as hereinafter provided, remaining unpaid, as certified to them by the collector, when the valuation list is completed, with interest to the date when interest on taxes becomes due and payable. At any time before the completion by the assessors of the valuation list for the year in which such assessments will first appear on the annual tax bill, the board of assessors may, and at the request of the owner of the land assessed shall, apportion all assessments or unpaid balances thereof made under this chapter into such number of equal portions, not exceeding twenty, as is determined by said board or as is requested by the owner, as the case may be, but no one of such portions shall be less than five dollars; provided, that, if an original assessment exceeds one hundred dollars and has been placed upon the annual tax bill, or has been apportioned into a number of portions less than twenty and the first portion has been placed upon an annual tax bill, the board of assessors may in its discretion, upon a request for the apportionment of such assessment into twenty portions made by the owner prior to a sale or taking of the land for the non-payment of such assessment or portion and upon payment of any necessary intervening charges and fees and such portions of such assessment as would have become due and payable if the request for apportionment had been seasonably made, apportion or reapportion the said assessment as aforesaid, and if any other tax or assessment constituting a lien upon the parcel to which the assessment so apportioned or reapportioned relates remains unpaid after such apportionment or reapportionment, the collector may institute proceedings anew for the sale or taking of such parcel at any time prior to the expiration of the lien or of a period of twenty days after such apportionment or reapportionment, whichever is the later. In any case in which an assessment relates to a state-funded project, the apportionment or reapportionment described herein shall be undertaken in accordance with the terms aforesaid by the board on whose behalf the assessment was made; provided, however, that the apportionment shall be made of said assessments or unpaid balances together with any interest due thereon. The assessors shall add one of said portions, with interest on the amount remaining unpaid from thirty days after the commitment of the original assessment to the collector to the date when interest on taxes becomes due and payable, to the first annual tax upon the land and shall add to the annual tax for each year thereafter one of said portions and one year's interest on the amount of the assessment remaining unpaid until all such portions shall have been so added; all assessments and apportioned parts thereof, and interest thereon as herein provided, which have been added to the annual tax on any parcel of land shall be included in the annual tax bill thereon. After an assessment or a portion thereof has been placed on the annual tax bill, the total amount of said bill shall be subject to interest under and in accordance with the provisions of section fifty-seven of chapter fifty-nine.
Notwithstanding a prior apportionment, the assessors, upon written application of the owner of the land assessed, shall order that the full amount, or any portion thereof, remaining unpaid of any assessment be payable forthwith and shall commit said amount, together with interest thereon from thirty days after the commitment of the original assessment if no portion has been added to a tax levy, or if a portion has been added to a tax levy, then with interest from October first of the year to which the last portion has been added, with their warrant therefor, to the collector for collection. If a part of a prior apportioned assessment is ordered to be payable forthwith, the payments shall be credited to the terminal or final years so as to reduce the period of payment.