A retroactive interest rate hike is when a lender increases the interest rate on an existing loan. This can happen at any time, but it is most commonly seen when the borrower is behind on their payments. When this happens, the lender will typically send a notice to the borrower informing them of the increase and giving them a specific deadline to pay the difference. A retroactive interest rate hike is when a credit card issuer raises the interest rate on your account after you have already been making payments at the lower rate. This practice was severely restricted by the Credit CARD Act of 2009, which requires issuers to give customers 45 days' notice before increasing rates.