N.Y. Comp. Codes R. & Regs. tit. 21, § 5002.3 – Payment for previous service for Tier 3 members who are eligible to purchase such service.

(a) The amount of money to be paid for previous service which was originally credited under a Tier 1 or Tier 2 membership shall be three percent of wages earned for such service.
(b) The amount of money to be paid for previous service which was originally credited under a Tier 3 membership be three percent of wages earned for such service, together with interest from the date of such service through the date of payment at the rate of five percent per annum compounded annually.
(c) The amount of money to be paid for previous service which was not previously credited in a public retirement system in New York State which predates the entry in the retirement system, pursuant to subdivision b of section 513 of the Retirement and Social Security Law, shall be three percent of wages earned for such service.