D.C. Mun. Regs. r. 1-1710
Interest shall be calculated at the rate of one percent (1%) per month.
Interest shall be computed from the day after the required payment through the actual payment date.
When an interest penalty that is owed is not paid, interest shall accrue on the unpaid amount until paid. Interest penalties remaining unpaid for any thirty-day (30) period will be added to the principal, and interest penalties thereafter, will accrue monthly on the total of principal and previously accrued interest.
When an agency takes a discount after the discount period has expired, the interest payment shall be calculated on the amount of the discount taken, for the period beginning the day after the end of the specified discount period through the actual payment date.
No interest penalties shall continue to accrue under the following circumstances:
Interest penalties of less than five dollars ($5.00) shall not be paid unless requested.
Adjustments shall be made for errors in calculating interest, if requested.
D.C. Mun. Regs. r. 1-1710