If you’re paying in chunks just pay attention to the information about application of payments and when the next payment is due.
Each time you satisfy a bill due, we will automatically advance your next payment due date and your billing statement will indicate a payment is not required for that bill. You may still continue to make payments to decrease your total interest cost and pay your loan off sooner. You have the option to select if you want your due date to be advanced on your loans. To request that all payments made over your monthly payment amount be applied to your current bill and not advance your due date, please see Submitting Special Payment Instructions.
https://www.mohela.com/DL/resourceCenter/HowPaymentsAreApplied.aspx