Interest Rate Differential Charge (IRC) – This is the amount of the charge that may apply if you pay down the principal before the maturity date or pay down more than the prepayment privilege. The amount of the interest rate differential charge is the difference between the amount of principal remaining to be repaid at the time of prepayment and the amount of principal that would remain to be repaid based on the rate of a similar loan. (It is important to analyze mortgage penalties as they vary by lender and type of loan.)