" This will lower your balance overall, and your interest payments going forward. When’s the best time to do that? Well, the day after your last payment was due.
That is, quite obviously, not possible for most people to do all of the time, especially if you’re struggling to make your minimum payment as it is. However, if you get a lump sum, say, with your tax refund, are able to save up an extra payment over the course of a few months or recently got a raise, you can make some real progress toward paying down your principal balance...."
https://twocents.lifehacker.com/schedule-an-extra-student-loan-payment-on-the-day-the-i-1832874931/a...
