Section 13-c - Interest rate on late payment of taxes and delinquencies(1) The amount of interest to be added on all taxes received after the interest free period and all delinquent taxes shall be one-twelfth the rate of interest as determined pursuant to subdivision two of this section.(2) On or before the fifteenth day of July in each year, the state commissioner of taxation and finance shall determine the one year constant maturity yield index for United States treasury securities for the quarter year ending on the immediately preceding June thirtieth. Such index, rounded to the nearest one-tenth of a percentage point, shall be the rate of interest prescribed by this subdivision, which rate shall be effective for all warrants issued for a collection period commencing on or after the first day of September next succeeding the date such rate of interest is determined provided, however, that such interest rate shall in no event be less than twelve percent per annum. In any given year for which the state commissioner of taxation and finance fails to determine the rate of interest by the preceding fifteenth day of July, the rate of interest determined for the prior year shall apply. For the purposes of this subdivision, the one year constant maturity yield index for United States treasury securities for any quarter year shall be the average of such index during the three months constituting such quarter year, as such index is compiled by the United States department of the treasury, published by the board of governors of the federal reserve system of the United States and expressed in terms of interest percentage per annum.N.Y. Suffolk County Tax Act § 13-c