Student Loan Interest Accrues Daily: Formula and Capitalization

Student loan interest accrues daily: a small charge attaches to your outstanding principal every day of the year, starting the moment your school receives the funds, and it keeps running through weekends, holidays, school breaks, and any period when no payment is due.¹ What determines whether that daily charge actually costs you more over time is a separate event called capitalization, when unpaid interest gets folded into your principal and starts generating interest of its own.

For loans disbursed in the 2025–2026 academic year, undergraduates pay 6.39%, graduate students 7.94%, and Parent PLUS borrowers 8.94%.² Those rates sit behind every calculation below.

The Daily Interest Formula

Federal and private student loans use simple daily interest. Servicers divide your annual rate by 365.25 (which accounts for leap years) to get a daily interest factor, then multiply that factor by your current principal balance.¹ Some private lenders divide by 365 instead, which produces a slightly higher daily charge.

Here is what that looks like with real numbers. An undergraduate with $30,000 in unsubsidized loans at 6.39% has a daily factor of about 0.0001749. Multiply that by $30,000 and the loan grows by roughly $5.25 a day, or about $158 a month.² A graduate student with the same balance at 7.94% picks up about $6.52 a day. Running the same math on your own balance tells you exactly how much the debt grows between payments.

How Accrual Changes With Your Loan Type and Status

Interest accrues every day on every student loan, but who pays for it varies by loan type and by what you are doing at the time.

Direct Subsidized Loans

Subsidized loans are the one place the federal government genuinely absorbs the cost. While you are enrolled at least half-time, during the six-month grace period after you leave school, and during authorized deferment periods, the Department of Education covers the interest, so your balance does not grow.³ Only undergraduates who show financial need qualify, and borrowing limits are lower than for unsubsidized loans, so most students carry some unsubsidized debt alongside them. Once you enter active repayment or go into forbearance, the subsidy ends and interest accrues like any other loan.

Direct Unsubsidized Loans and Private Loans

These loans offer no interest-free periods at all. Interest starts the day funds are disbursed and continues through every phase: in school, grace period, deferment, and forbearance.¹ A borrower who takes out $20,000 in unsubsidized loans as a freshman at 6.39% will build up roughly $4,670 in interest by graduation, before making a single payment.

Parent PLUS Loans

Parent PLUS loans carry the highest federal rate (8.94% for 2025–2026 disbursements) and receive no interest subsidy during any period.³ Parents can defer payments while the student is enrolled at least half-time and for six months after, but interest piles up the whole time. On a $50,000 Parent PLUS loan, that works out to about $12.23 a day, or close to $18,000 of interest across a four-year deferment.

When Unpaid Interest Capitalizes

Capitalization is the point at which accumulated unpaid interest gets added to your principal. After that happens, the daily interest calculation runs against a larger number, and you start paying interest on old interest. This is the compounding event that makes balances balloon.

For federal Direct Loans, capitalization is more limited than many borrowers assume. Interest that builds up during the grace period, while you are in school, or during forbearance no longer automatically capitalizes when those periods end.⁴ The unpaid interest stays on your account as a separate line item instead of merging into principal.

Capitalization still happens on Direct Loans in these situations:

When a deferment period ends on an unsubsidized loan, any accrued interest capitalizes.⁵
On Income-Based Repayment, unpaid interest capitalizes if you voluntarily switch to a different plan, miss your annual recertification deadline, or no longer qualify for a reduced payment after recertification.⁵
When you consolidate federal loans into a Direct Consolidation Loan, the new principal equals the sum of the balances paid off, which includes all accrued interest on the originals.⁶

Older FFEL loans that are not held by the federal government may still capitalize interest at the end of a grace period, after certain forbearance types, or when exiting IBR.⁴ If you are not sure which type of loan you hold, your servicer can tell you.

What Capitalization Actually Costs

Say you have an unsubsidized loan with a $20,000 balance at 6.39% and you enter a six-month deferment. About $640 of interest accrues during those six months. If it capitalizes, your new principal becomes $20,640, and daily interest from that point forward runs against the larger number, adding roughly $0.11 extra every day. Spread across a 10-year repayment, and compounded by any later capitalization events, that quietly adds hundreds of dollars to the loan.⁵

Changes Coming Under the One Big Beautiful Bill Act

The rules governing when interest capitalizes are shifting. The One Big Beautiful Bill Act, signed in July 2025, phases out several income-driven plans and creates new ones.⁷

For loans disbursed on or after July 1, 2026, the SAVE plan is no longer available. The PAYE and ICR plans sunset on June 30, 2028, for most borrowers. New borrowers will choose between a modified standard repayment plan and the new Repayment Assistance Plan (RAP). RAP is designed to prevent negative amortization: the government subsidizes any monthly interest your payment does not cover and contributes up to $50 toward principal for each on-time payment. If you do not make an on-time payment that covers accrued interest, unpaid interest capitalizes under this plan.⁷

Starting July 1, 2027, new Direct Loan borrowers will also lose access to unemployment and economic hardship deferments, removing one source of interest buildup that would otherwise capitalize on exit.⁷ Existing borrowers keep their current plan options for now. The details are still being worked out through rulemaking and may shift before they take full effect.

How to Keep Interest From Compounding Against You

The most effective move is also the simplest: pay interest before it capitalizes. You do not have to wait for your first bill. During the grace period, deferment, or any other non-payment stretch, you can make interest-only payments to your servicer to keep the balance flat.⁸ Even partial payments help. On a $30,000 unsubsidized loan at 6.39%, full monthly interest runs about $158; paying half of that still slows the snowball meaningfully.

If you are on an income-driven plan, never miss your annual recertification deadline. Missing it triggers capitalization and can spike your monthly payment.⁹ Set a calendar reminder at least 30 days ahead. Servicers send notices, but those are easy to miss when contact information is outdated.

Think carefully before consolidating. Consolidation bakes all your accrued interest into the new principal, which is a permanent capitalization event. If you are carrying a large amount of unpaid interest, paying it down first saves you money over the life of the new loan.

1
Edfinancial Services. Payments, Interest, and Fees
2
Federal Student Aid. Interest Rates for Direct Loans First Disbursed Between July 1, 2025 and June 30, 2026
3
MOHELA – Federal Student Aid. I’m a Parent Borrower
4
Consumer Financial Protection Bureau. Tips for Paying Off Student Loans More Easily
5
Nelnet – Federal Student Aid. Interest Capitalization
6
eCFR. 34 CFR 685.220 – Consolidation
7
Regulations.gov. Reimagining and Improving Student Education
8
MOHELA – Federal Student Aid. Borrower In Grace
9
MOHELA. Income-Driven Repayment (IDR) Plans