If a person or corporation contracts in the District, (1) verbally, to pay a greater rate of interest than 6% per annum, or (2) in writing, to pay a greater rate than is permitted under section 28-3301, 28-3308, under Chapter 36 of this subtitle, or under § 26-301 et seq., the creditor shall forfeit the whole of the interest so contracted to be received. This section does not affect sections 26-901 to 26-912 .
Usury defined
D.C. Code § 28-3303, under Interest and Usury..
D.C. Code § 28-3303