How interest accrues on your student loans
Student loan interest is calculated daily based on your outstanding balance, the interest rate on your loan, and the type of loan you have. The formula is straightforward: your daily interest equals your loan balance multiplied by your annual interest rate, then divided by 365. That daily amount compounds — meaning interest accrues on top of previous interest — until you make a payment.
The timing of when interest starts to accrue depends on your loan type. Federal subsidized loans do not accrue interest while you are in school at least half-time, during your grace period, or during deferment. Federal unsubsidized loans and private loans accrue interest from the moment they are disbursed, even if you are still in school and not yet making payments. If you do not pay accrued interest as it builds, it capitalizes — meaning it gets added to your principal balance — and you then pay interest on that interest.
Your interest rate is fixed for the life of most federal loans, though the rate varies depending on when you borrowed and what type of loan you have. Private student loans may have fixed or variable rates, and variable rates can change over time based on market conditions.
Key Takeaways
- Daily interest is calculated by multiplying your loan balance by your annual interest rate and dividing by 365.
- Federal subsidized loans do not accrue interest while you are in school, but unsubsidized and private loans accrue interest immediately.
- Unpaid interest capitalizes when you enter repayment, meaning you will owe interest on top of interest if you do not pay it down first.
- Your total interest paid depends on your repayment plan, how long you take to repay, and whether you make extra payments toward principal.
The difference between subsidized and unsubsidized federal loans
With a subsidized loan, the federal government pays the interest that accrues while you are in school, during your grace period, and during certain deferment periods. You only owe the principal amount you borrowed. This means if you borrowed $10,000 at 5.5 percent, you repay $10,000 plus interest that accrues only after you leave school or drop below half-time enrollment.
With an unsubsidized loan, you are responsible for all interest from the day the loan is disbursed. If you do not pay that interest while in school, it capitalizes when you enter repayment. If you borrowed $10,000 at 6.33 percent and were in school for four years without paying interest, roughly $2,800 in accrued interest would be added to your principal. You would then repay approximately $12,800 plus additional interest on that larger amount.
The difference in total cost is significant over a 10-year repayment period. On a $10,000 unsubsidized loan at 6.33 percent with capitalized interest, you might pay roughly $3,500 in total interest. On the same subsidized loan, you would pay roughly $1,700 in total interest, because interest only accrues after you leave school.
How repayment plans affect your total interest
Your repayment plan determines how much you pay each month and how long you take to repay, which directly changes how much interest you pay overall. The standard 10-year plan has fixed monthly payments and the least total interest. Income-driven plans like PAYE, REPAYE, IBR, and ICR have lower monthly payments but extend repayment to 20 or 25 years, meaning you pay far more interest over time.
On a $30,000 federal loan at 5.5 percent, the standard 10-year plan costs roughly $9,000 in total interest. The same loan on PAYE, with a lower monthly payment, might cost $15,000 or more in total interest because you are repaying over 25 years instead of 10. However, income-driven plans forgive remaining balance after the repayment period ends, which may make the lower payment worth the extra interest if your income is low.
Making extra payments toward principal reduces your balance faster and cuts total interest significantly. Even an extra $50 per month on a $30,000 loan can save you $2,000 or more in interest and shorten your repayment by one to two years.
Calculating interest on private student loans
Private loans use the same daily interest formula as federal loans, but the terms vary widely by lender. Your interest rate depends on your credit score, income, and the lender's policies. Rates can be fixed or variable, and variable rates reset periodically — usually annually — based on an index like the prime rate.
To calculate your daily interest on a private loan, multiply your current balance by your annual interest rate and divide by 365. If you have a $25,000 private loan at 7 percent, your daily interest is roughly $4.79. Over a month, that is approximately $144 in interest before any principal is paid down.
Private loans do not have grace periods or deferment options like federal loans do. Interest accrues from disbursement, and if you do not pay it while in school, it capitalizes when repayment begins. Some private lenders allow you to make interest-only payments while in school to prevent capitalization, but you have to request this option.
What happens when interest capitalizes
Capitalization occurs when unpaid interest is added to your principal balance. This happens automatically at specific points: when you leave school on an unsubsidized loan, when you exit deferment or forbearance, or when you transition from an income-driven plan to standard repayment on federal loans. On private loans, capitalization happens when you enter repayment or when your lender decides to capitalize accrued interest.
Capitalization increases the amount you owe and the interest you pay going forward, because you now pay interest on a larger principal. On a $15,000 unsubsidized loan with $2,000 in capitalized interest, you repay $17,000 plus interest on that $17,000. Over 10 years, that extra $2,000 in principal can cost you an additional $1,000 or more in interest.
You can prevent or reduce capitalization by paying accrued interest before it capitalizes. If you have unsubsidized loans and are still in school, paying even small amounts toward interest keeps it from building up. Some borrowers pay interest-only while in school, then switch to full principal-and-interest payments after graduation.
Using loan calculators to estimate your interest
The Federal Student Aid website offers a loan payment calculator where you enter your loan amount, interest rate, and repayment plan to see estimated monthly payments and total interest. You input your current balance, annual interest rate, and years to repayment, and the calculator shows you the total amount you will pay and how much of that is interest.
Private lenders usually have calculators on their websites as well. These tools let you compare what different interest rates or repayment lengths would cost. A calculator cannot predict what your income will be or whether you will make extra payments, but it gives you a realistic baseline for planning.
When using a calculator, remember that the result assumes you make on-time payments for the full term. If you use an income-driven plan, your actual payment may be lower than the calculator shows, but your total interest will be higher because repayment takes longer. If you plan to make extra payments, the calculator will overestimate your total interest.
Frequently Asked Questions
How do I know if my loan is subsidized or unsubsidized?
Log into your Federal Student Aid account at studentaid.gov and view your loan details. Subsidized loans will be labeled as "Subsidized Stafford" or "Subsidized Direct Loan." Unsubsidized loans are labeled "Unsubsidized Stafford" or "Unsubsidized Direct Loan." Your loan servicer can also tell you over the phone.
Can I pay interest while I'm still in school to avoid capitalization?
Yes. You can make voluntary interest payments on unsubsidized loans while in school, and most servicers accept them. Contact your servicer to confirm they will credit payments toward interest rather than principal, so the payment actually prevents capitalization instead of just reducing your balance.
Does interest accrue during forbearance or deferment?
On subsidized loans, interest does not accrue during deferment but does accrue during forbearance. On unsubsidized loans and private loans, interest accrues during both. Any unpaid interest capitalizes when the forbearance or deferment period ends.
What's the difference between fixed and variable interest rates?
A fixed rate stays the same for the life of the loan. A variable rate changes periodically, usually once per year, based on market conditions. Variable rates are typically lower at first but can rise significantly over time, making your monthly payment and total interest unpredictable.
If I pay extra toward my loan, does it reduce the interest I owe?
Yes. Extra payments go toward principal, which reduces your balance and the amount of interest that accrues daily. The sooner you pay down principal, the less total interest you pay over the life of the loan and the faster you finish repayment.