N.Y. Personal Property Law § 410
1. A retail instalment contract or obligation which otherwise conforms to the requirements of this article may contain the promise or agreement of the buyer to pay in substantially equal periodic instalments the consolidated total of the principal balance thereof and the unpaid time balance or balances owing by the buyer under one or more previous contracts or obligations, together with a credit service charge; if it does so:
(b) Subject to the provisions of section four hundred four and to the provisions of paragraph (c) of this subdivision, the credit service charge to be included in such consolidated total may equal but shall not exceed the larger of the amounts determined by applying the credit service charge at the rate or rates agreed to by the buyer: