Interest is money you pay the lender on top of what you borrowed

When you borrow money for school, you agree to pay back the amount you borrowed plus interest. Interest is a percentage of your loan balance that accrues — meaning it grows — over time. The lender charges this as the cost of lending you money. On a $10,000 loan at 5% interest, you will owe more than $10,000 by the time you finish repaying.

How much interest you pay depends on three things: the size of your loan, the interest rate, and how long you take to repay. A loan with a higher rate or a longer repayment period will cost you significantly more in interest alone. Federal student loans and private student loans calculate and charge interest differently, so the type of loan you have matters.

Key Takeaways

  • Interest accrues daily on most student loans, meaning it grows every single day based on your current balance and interest rate.
  • Federal loans have fixed interest rates set by Congress, while private loans have rates that may be fixed or variable and depend on your credit.
  • Unsubsidized federal loans charge interest while you are still in school; subsidized federal loans do not accrue interest until after you graduate.
  • Interest that accrues but is not paid can capitalize — meaning it gets added to your principal balance — and then you owe interest on the interest.
  • Making payments while in school or during grace periods can prevent interest from capitalizing and reduce what you ultimately owe.

How interest accrues on federal loans versus private loans

Federal student loans have interest rates set by Congress. For loans issued in the 2024–2025 school year, the rate is fixed at 8.5% for undergraduate loans and varies slightly for graduate and Parent PLUS loans. These rates do not change over the life of the loan. Interest accrues daily, meaning each day a small amount of new interest is added to what you owe.

Private student loans are issued by banks, credit unions, and other lenders. Their interest rates depend on your credit score and history. Private rates can be fixed (staying the same for the entire loan) or variable (changing based on market conditions). Private lenders set their own rates, so two borrowers with different credit scores will pay different rates on the same loan amount. Private loans also accrue interest daily.

The key difference: federal rates are the same for everyone in a given year, while private rates vary by borrower. This means you cannot shop around to lower a federal rate, but you can compare private lenders before borrowing.

Subsidized versus unsubsidized federal loans

Subsidized federal loans do not accrue interest while you are in school at least half-time, during your six-month grace period after graduation, or during certain deferment periods. The federal government pays the interest for you during these times. When you enter repayment, interest begins to accrue on the remaining balance.

Unsubsidized federal loans accrue interest from the moment the loan is disbursed — even while you are in school. Interest continues to build during your grace period and any deferment. If you do not pay this accrued interest before repayment begins, it capitalizes.

This is a real difference in cost. On a $10,000 unsubsidized loan at 8.5% interest, roughly $850 in interest will accrue during a four-year undergraduate program and six-month grace period. If that interest capitalizes, you will owe interest on $10,850 instead of $10,000 for the rest of your repayment.

What capitalization means and when it happens

Capitalization is when unpaid interest gets added to your principal balance — the original amount you borrowed. Once interest is capitalized, you owe interest on that interest going forward. This compounds your debt.

On federal loans, capitalization typically happens at these points:

  • When you enter repayment after graduation or dropping below half-time enrollment.
  • When a deferment or forbearance period ends.
  • When you switch repayment plans.
  • When a loan is consolidated into a Direct Consolidation Loan.

On private loans, capitalization rules vary by lender. Some capitalize interest monthly, others only when you miss a payment or exit school. Check your loan documents or contact your lender to know when capitalization occurs on your specific loan.

How to calculate what you will owe in interest

Interest accrues daily using this formula: (Loan Balance × Interest Rate) ÷ 365 = Daily Interest. If you have a $20,000 loan at 6% interest, the daily interest is ($20,000 × 0.06) ÷ 365 = $3.29 per day. Over a year with no payments, that is roughly $1,200 in interest.

The total interest you pay over the life of the loan depends on your repayment plan. A standard 10-year repayment plan on a $30,000 federal loan at 8.5% will cost roughly $9,000 in interest. An income-driven repayment plan that stretches payments over 20 or 25 years will cost significantly more in total interest, because interest accrues for a longer period. However, your monthly payment will be lower.

You can estimate your total interest using the federal student loan repayment calculator at studentaid.gov, or ask your lender for a repayment schedule that shows exactly how much interest you will pay under each plan option.

Strategies to reduce the interest you pay

Pay interest while in school if you can. Even small payments on unsubsidized loans prevent interest from capitalizing. A $50 payment per semester on a $10,000 unsubsidized loan saves you roughly $200 in capitalized interest over the life of the loan.

Make extra payments toward principal once you are in repayment. Any payment above your required monthly amount goes directly to reducing your balance, which means less interest accrues going forward. Paying an extra $100 per month on a $30,000 loan can cut years off your repayment and save thousands in interest.

Choose a shorter repayment plan if your budget allows. The standard 10-year plan costs less in total interest than a 20-year income-driven plan, even though your monthly payment is higher. If you can afford it, this is the cheapest option overall.

Refinance private loans if your credit improves. If you took out private loans with a high rate and your credit score has risen, you may be able to refinance at a lower rate with a different lender. This does not work for federal loans — refinancing a federal loan into a private loan is permanent and you lose federal protections.

What happens if you do not pay accrued interest

If you do not pay interest that has accrued on your loan, it capitalizes when you enter repayment or when a deferment ends. Your new loan balance becomes higher, and you owe interest on the larger amount. This is why paying even small amounts during school or grace periods matters — it stops interest from compounding.

If you miss payments after repayment begins, interest continues to accrue on the unpaid balance. Late fees may also apply on private loans. On federal loans, missing payments triggers default after 270 days, which has serious consequences including wage garnishment and loss of may be able to access for future federal aid.

Frequently Asked Questions

Does interest accrue on student loans while I am in school?

It depends on the loan type. Subsidized federal loans do not accrue interest while you are in school. Unsubsidized federal loans and all private loans accrue interest from day one, even while you are enrolled. The accrued interest on unsubsidized loans will capitalize when you enter repayment unless you pay it off first.

Can I pay just the interest on my student loans?

Yes. Many borrowers pay only accrued interest while in school to prevent capitalization. Once you are in repayment, your required payment covers both interest and principal. You can always pay more than required, and any extra goes toward principal.

What is the difference between a fixed and variable interest rate?

A fixed rate stays the same for the entire life of the loan. A variable rate changes based on market conditions, usually annually. Federal loans have fixed rates. Private loans may offer either. Variable rates start lower but can increase, making your payment unpredictable.

If I refinance my federal loan into a private loan, do I lose anything?

Yes. You lose federal protections including income-driven repayment plans, deferment and forbearance options, and Public Service Loan Forgiveness. Refinancing is permanent — you cannot convert back to federal status. Only refinance if you have stable income and do not need federal safety nets.

How much will I pay in total interest on my student loans?

It varies based on your loan amount, interest rate, and repayment plan. Use the federal calculator at studentaid.gov or ask your lender for a repayment schedule. A rough estimate: on a $30,000 loan at 8.5% over 10 years, you will pay roughly $9,000 in interest. Over 20 years, it could be $18,000 or more.