Capitalized interest
Unpaid interest that gets added to the principal balance, increasing the loan's true size. Common on student loans during deferment.
Reviewed May 2026.
When interest accrues but isn't paid, the lender can 'capitalize' it — adding it to the principal balance. After capitalization, you're now paying interest on the original principal AND on the previously-unpaid interest. The loan effectively grows.
This happens most often with student loans during forbearance or deferment, but also on construction loans during the build phase, certain reverse mortgages, and some negative-amortization adjustable-rate mortgages (rare since 2008).
Capitalization is usually triggered by specific events spelled out in the loan agreement: end of grace period, end of forbearance, change in repayment plan. Once capitalized, that interest is now principal and behaves like principal forever — you can't 'uncapitalize' it.
On federal student loans, current capitalization triggers and unpaid-interest treatment depend on the specific repayment plan. The SAVE plan was placed under court order on March 10, 2026 and is no longer an available IDR option; current Federal Student Aid IDR guidance lists IBR, ICR, and PAYE. For your loan's current capitalization and unpaid-interest treatment, check StudentAid.gov and your servicer dashboard — the rules have shifted multiple times during the SAVE litigation cycle.
PayoffMath angle. On a loan with capitalized unpaid interest, the principal you pay future interest against is higher than the original loan amount — extras need to clear the capitalized portion before the lifetime-interest math from a standard payoff calculator starts behaving normally.
Why it matters. Capitalization quietly grows the loan after the fact. Borrowers who think 'I borrowed $30,000' often owe meaningfully more by the time repayment starts, and the bigger principal sets a higher interest-charge baseline for every future month.
Common mistake. Assuming the capitalized interest is reversible. Once added to principal, that balance behaves like any other principal — you can't 'uncapitalize' it. The right time to keep interest from capitalizing is during the in-school, grace, or forbearance window, by paying just the accruing interest each month.
Try the student loan payoff calculator → — model how a post-deferment capitalization event changes the payoff date and total interest on a federal Direct loan.
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Sources and review
Reviewed May 2026. Glossary entries are plain-language definitions, not legal definitions. For account-specific rules, your loan documents control.
Definition by James L. Wu. Plain-language gloss, not a legal definition. For terms that show up in your loan paperwork, the governing language is in your loan documents. See the editorial policy for sourcing.