how about the statement below? (from an article) and what would the current interest rate be?

Care must be given, however, to ensure that the proprietary lease authorizes those particular charges, otherwise the co-op opens itself up to counter-claims by the shareholder and for his or her legal fees, if the shareholder is successful.

The most common abuse by co-ops is the inclusion of cumulative late charges, such as $25 the first month, $50 the second month, $75 the third month and so on.

This type of late charge structure violates not only most proprietary leases (which provide that late fees can only be charged equal to the maximum legal rate of interest), but also violates usury laws. Since the purpose of the rent demand, or "Notice to Cure," is to afford the shareholder the opportunity to determine the claim’s accuracy, only those charges which are legal and permissible should be included in the notice.