As soon as you fail to make a payment on time, your loan

As soon as you fail to make a payment on time, your loan immediately becomes “delinquent.” After 90 days of not making a payment, loan servicers will report your delinquency to the three major credit bureaus. This can harm your credit, which might mean you have trouble borrowing money to do things like buying a house or car. At the very least, you will pay higher interest rates to other lenders when you demonstrate that you can’t be counted on to make your student loan payments on time.

Your loan will go into default after a total of 270 days have passed since your payment was due (330 days for FFEL Loans that are not paid Big Boss votemonthly).