How Does Student Loan Interest Work?
Updated July 9, 2026 · SmartRates Editorial Team
⚡ In short
Federal student loan interest accrues daily, calculated from the loan's outstanding principal and its fixed annual interest rate. Direct Subsidized Loans do not accrue interest while the borrower is in school at least half-time or during the grace period; Direct Unsubsidized Loans and most private loans accrue interest continuously from disbursement.
📌 Key facts
- Federal student loan interest rates are fixed for the life of the loan and set annually by Congress
- Unpaid interest can be added to the loan's principal balance in a process called capitalization
- Direct Subsidized Loans don't accrue interest during in-school, grace, and deferment periods; Direct Unsubsidized Loans do
- Private student loans may carry fixed or variable rates set by the individual lender
🏛️ Official sources
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Daily interest accrual
Federal student loan interest is calculated using a simple daily interest formula: outstanding principal multiplied by the loan's fixed interest rate, divided by the number of days in the year, producing the amount of interest that accrues each day. This daily amount is often referred to as the loan's daily interest rate factor, and it's multiplied by the number of days since the last payment to determine the interest portion of a scheduled payment.
Subsidized vs. unsubsidized loans
Direct Subsidized Loans, available to undergraduate students with demonstrated financial need, do not accrue interest while the borrower is enrolled at least half-time, during the six-month grace period after leaving school, and during certain deferment periods. Direct Unsubsidized Loans accrue interest continuously from the date of disbursement, regardless of enrollment status, and are available to both undergraduate and graduate students without a demonstrated-need requirement.
Capitalization — when unpaid interest is added to principal
Capitalization occurs when accrued, unpaid interest is added to a loan's principal balance, typically at points such as the end of a grace period, deferment, or forbearance, or upon leaving certain repayment plans. After capitalization, future interest is calculated on the new, higher principal balance, which means the same interest rate produces a larger dollar amount of interest going forward than it would have on the original, lower principal.
Federal vs. private loan rate-setting
Federal student loan interest rates are set annually by Congress and apply uniformly to loans disbursed within a given period, remaining fixed for the life of that loan. Private student loan lenders set their own rates individually, which may be fixed or variable, based on the lender's underwriting criteria, including the applicant's or cosigner's credit profile — a key difference from federal loans, which do not use a credit-based rate for most loan types.
Servicer role in interest calculation
A loan servicer — the company that manages billing and payment processing on behalf of the federal government or a private lender — calculates the specific daily accrual and applies payments according to the loan's terms. The servicer does not set the interest rate itself; it administers the loan under the rate and terms already established at origination.
How payments are applied across multiple loans
A borrower with multiple federal student loans, each potentially carrying a different interest rate from different disbursement years, has payments allocated according to the servicer's standard allocation method unless the borrower provides specific payment instructions, subject to the servicer's rules for accepting such instructions. Because different loans in the same borrower's portfolio can carry different rates, understanding how a servicer allocates a payment across those loans affects how quickly interest accrues on each one.
Interest paid on federal loans and tax reporting
Interest paid on federal or private student loans during the year is reported to the borrower by the servicer on Form 1098-E if the amount paid meets a reporting threshold, which can be used when preparing a federal tax return, since student loan interest may be deductible up to an annual limit and subject to income phase-outs set by the IRS.
How refinancing changes the interest calculation
Refinancing a student loan — replacing one or more existing loans with a new private loan, typically to obtain a different rate or term — resets the interest calculation entirely, since the new loan uses its own rate and daily accrual starting from the refinance date. Refinancing federal loans into a private loan also means giving up federal-loan-specific features, including eligibility for federal income-driven repayment plans and federal forgiveness programs, since those programs apply only to federal loans.
Frequently Asked Questions
Does interest accrue on a student loan while still in school?+
It depends on the loan type. Direct Subsidized Loans do not accrue interest during in-school enrollment (at least half-time); Direct Unsubsidized Loans accrue interest continuously from disbursement, including while enrolled.
What happens to unpaid interest when a loan enters repayment?+
Unpaid accrued interest is commonly capitalized — added to the principal balance — at the point repayment begins, after which future interest is calculated on the new balance.
Are federal student loan interest rates the same for every borrower?+
Federal rates are set annually by Congress and apply to all loans of that type disbursed within the applicable period, regardless of the individual borrower's credit profile.
Does a loan servicer set the interest rate on a student loan?+
No. A servicer administers billing and payment processing under the rate and terms already set at origination — it does not set or change the interest rate itself.
Are graduate students eligible for Direct Subsidized Loans?+
No. Direct Subsidized Loans are limited to undergraduate students with demonstrated financial need; graduate students may be eligible for Direct Unsubsidized Loans, which accrue interest continuously from disbursement.
Does refinancing a federal student loan into a private loan change how interest accrues?+
Yes. The new private loan uses its own rate and daily accrual calculation starting from the refinance date, and it also forfeits federal-loan-specific repayment and forgiveness options going forward.
Is the daily interest formula the same for federal and private student loans?+
The general daily-accrual mechanic — principal multiplied by rate, divided by days in the year — is common to both, though private lenders may structure specific terms, such as compounding frequency, differently from federal loan servicing rules.
Does a payment made mid-cycle stop interest from accruing on that portion right away?+
Yes — once a payment is applied, interest going forward accrues only on the remaining outstanding principal, since the daily calculation is based on the current balance at any given point in time.