There could be many reasons for this, but it's likely due to capitalized interest.
Interest accrues daily on student loans and Unpaid Interest may be capitalized (added to the principal balance) as permitted
by law and your loan agreement.
Capitalized interest increases both the principal balance and total loan cost.
Typically, interest may be capitalized at the end of a grace/deferment/forbearance period or when the loan enters repayment
(as often as quarterly during in-school, grace, or deferment periods).
Tip! You can help avoid capitalized interest by making interest payments even when you don't have payments
required (e.g., in school) or avoiding deferment and forbearance options altogether.
To view a full transaction history, log in to your MOHELA online account and go to your "Account History". From there you
can review how past payments were applied (typically applied to Unpaid Fees, then Unpaid Interest, and lastly Unpaid
Principal), fees assessed, and changes to your balance (including capitalized interest).