Clause Twenty-second of section 5 of chapter 59 of the General Laws, as appearing in the 2018 Official Edition, is hereby amended by adding the following subsection:-

(h) The assessors shall calculate a proportionate addition to the amount of the exemption to be added to the exemption allowed under subsections (a) to (f), inclusive, by making the following calculations:-

(1) Determine the amount of exemption under said clause;

(2) Then, determine the amount of property taxes due from the applicant from the prior tax year, without exemption; and

(3) Then, determine the amount of property taxes due from the applicant in the current tax year, without exemption.

(4) If the amount in subdivision (3) is greater than the amount in subdivision (2), subtract the amount in subdivision (2) from the amount in subdivision (3).

(5) Determine the percentage increase in taxes by dividing the amount in subdivision (4) by the amount in subdivision (2) and multiply the result by 100.

(6) Multiply the percentage increase under subdivision (5) by the amount under subdivision (1), which shall be the proportionate addition to the amount of exemption allowed under said clauses.

The total amount in subdivision (6) shall be added to the exemption in subdivision (1) under said subsections (a) to (f), inclusive, and shall be newly calculated annually.