Here's the definition of the US Rule in case anyone needs it:

The US Rule determines interest paid on the loan after a partial payment is made before the due date of the loan. The partial payment pays the interest first for that given time and then a part of the principal. The interest for the remaining part of the loan is calculated on the new principal and the days since the partial payment. When applying the US Rule, the Banker's Rule is used to calculate the interest (360 days = 1 year and any fractional part of a year = exact number of days.)