Student loan balances frequently exceed the amount originally borrowed. Capitalization, the addition of accrued unpaid interest to principal, is the mechanism behind that growth.
Interest accrues before repayment begins
Unsubsidized federal loans and most private loans accrue interest from disbursement, including during enrollment. The borrower is not required to pay it during that period, but it accumulates.
Subsidized federal loans differ: the government covers interest during defined periods, so nothing accrues to the borrower's account then.
The distinction is why two borrowers with identical principal can enter repayment with very different balances.
Capitalization converts interest into principal
Accrued interest sits separately until a triggering event occurs. At that point it is added to the principal balance, and subsequent interest is calculated on the larger figure.
The effect compounds only at those events rather than continuously, so the number of triggers over a loan's life matters as much as the rate.
Once capitalized, the amount cannot be separated out again. It is principal for every purpose thereafter.
Specific events trigger it
Typical triggers include entering repayment after a grace period, the end of a deferment or forbearance, a change in repayment plan, and loan consolidation.
Legislation and regulation have narrowed the list of triggers for federal loans over recent years, removing some events that previously caused capitalization.
Private loan terms vary by lender, and the promissory note is the document that governs which events apply to a particular loan.
Payment allocation determines what shrinks
A payment is generally applied first to fees, then to accrued interest, then to principal. A payment smaller than the accrued interest reduces no principal at all.
Under income-driven arrangements a required payment can be below accruing interest, producing negative amortization in which the balance grows despite payments being made on time.
Some federal programs address this by subsidizing or preventing accrual of the unpaid difference, and the terms differ by plan.
Prepayment and interest timing interact
Because interest accrues daily on the outstanding principal, paying earlier in a cycle or paying while interest is uncapitalized reduces the base on which future interest builds.
Federal loans carry no prepayment penalty, so extra payments reduce principal directly once accrued interest is satisfied, provided the servicer is instructed accordingly.
Loan terms, program rules and eligibility change frequently, so the servicer and current federal guidance are the appropriate sources for any individual account.