How does student loan interest work? See daily interest, monthly accrual, and your payoff split
Student loans accrue interest daily on a simple-interest basis: daily interest = balance x (annual rate / 365). A $30,000 balance at 6.53% grows $5.37 a day, about $161 a month, or $1,959 a year. On the 10-year standard plan the payment is $341.10, and on day one $163.25 of it, 48%, is interest while only $177.85 touches principal. Total interest over the full payoff: $10,932, or 36% of what you borrowed. Unpaid interest capitalizes at capitalization events (leaving school, exiting most income-driven plans, forbearance end), which adds it to principal so it earns interest itself.
Not sure of the payment? The 10-year standard plan on $30,000 at 6.53% is $341.10. Enter any payment to model extra payments or income-driven plans.
| Academic Year | Direct Subsidized / Unsubsidized (Undergrad) | Grad Unsubsidized | Direct PLUS |
|---|---|---|---|
| 2020-21 | 2.75% | 4.30% | 5.30% |
| 2021-22 | 3.73% | 5.28% | 6.28% |
| 2022-23 | 4.99% | 6.54% | 7.54% |
| 2023-24 | 5.50% | 7.05% | 8.05% |
| 2024-25 | 6.53% | 8.08% | 9.08% |
| 2025-26 | 6.39% | 7.94% | 8.94% |
Federal rates reset every July 1 from the May 10-year Treasury auction plus a fixed add-on, and they're locked for the life of each loan. That's why a borrower who started in 2020-21 pays 2.75% while a 2024-25 borrower pays 6.53% on the same type of loan. Private loans range roughly from 4% to 18% depending on credit.
| Balance | Daily Interest | per 30-Day Month | per Year |
|---|---|---|---|
| $10,000 | $1.79 | $54 | $653 |
| $20,000 | $3.58 | $107 | $1,306 |
| $30,000 | $5.37 | $161 | $1,959 |
| $50,000 | $8.95 | $268 | $3,265 |
Every dollar of balance accrues the same rate, which is why the numbers scale linearly. A useful gut check: at 6.53%, each $10,000 of balance costs $1.79 a day in interest, 54 cents of it while you sleep.
Student loans use daily simple interest, not the compound interest of credit cards. Each day, the servicer accrues one day of interest on your current principal. Nothing compounds, because accrued interest is paid off with each payment before it can join the balance. The exception is capitalization, covered below.
Daily interest = balance x (annual rate / 365). Monthly accrual is that daily figure times the days in the month, so February is slightly cheaper than March. Your payment applies in a fixed order: fees, then accrued interest, then principal. Interest share of a payment = accrued interest / payment.
For the payoff math, the calculator amortizes month by month: each payment covers that month's accrual first, the remainder reduces principal, and the loop runs until the balance hits zero.
Enter your current balance from your servicer's dashboard (not the original amount you borrowed), your rate, and your payment. The daily and monthly numbers come straight from the formula. The payoff and total-interest figures amortize your exact payment, so you can test extra payments: bump the payment $50 and watch the total interest fall.
Borrower A owes $30,000 at 6.53% and is on the standard 10-year plan. Payment: $341.10. Day one accrual: 30,000 x 0.0653 / 365 = $5.37, which is $161 over a 30-day month. The first payment sends $163.25 to interest (one month at the monthly equivalent rate) and $177.85 to principal, so 48% of the payment is interest. Run the schedule to month 120 and total interest is $10,932, 36.4% of the amount borrowed. Adding $50 a month pays it off in 100 months instead of 120 and saves about $2,000 in interest.
Borrower B is still in school with $27,000 of unsubsidized loans at 6.53%, disbursed evenly over four years and accruing until the end of her six-month grace — an average of about 30 months per dollar. Simple interest, no compounding, still adds up: roughly $4,400 capitalizes at graduation, making the balance about $31,400. Her standard payment jumps from $306.99 (had interest never accrued) to about $357, a $50-a-month penalty for four and a half years of accrual. Subsidized loans don't have this problem; the government covers interest during school.
One habit worth stealing from the payoff crowd: pay accrued interest before it capitalizes. A payment made during deferment goes 100% to principal once current interest is cleared, which is the cheapest dollar you'll ever spend on a student loan.
Federal student loans accrue interest daily using simple interest: daily interest = balance x (annual rate / 365). A $30,000 balance at 6.53% grows $5.37 a day. Payments are applied to interest first, then fees, then principal. Unlike a mortgage, there's no compounding unless unpaid interest capitalizes, which happens when you leave deferment, forbearance, or most income-driven plans.
Multiply the balance by the annual rate, divide by 365, then multiply by the days in the month. On $30,000 at 6.53%, that's $5.37 a day, about $161 in a 30-day month and $166 in a 31-day month. Over a full year the balance accrues $1,959 at that rate.
Amortization. Each payment covers the interest accrued that month first, and whatever is left chips away at principal. Early on the balance is largest, so the interest share is largest: on $30,000 at 6.53% with a $341.10 standard payment, the first payment is 48% interest. As principal shrinks, the interest share falls and more of the same payment goes to principal.
On unsubsidized and PLUS loans, yes, from the day funds are disbursed. On subsidized loans, the government pays the interest while you're enrolled at least half-time, during the 6-month grace period, and during qualifying deferment. Unpaid unsubsidized interest capitalizes, which is why a $27,000 loan disbursed over four years of school can grow by about $4,400 — to roughly $31,400 — by graduation on a 6.53% undergrad rate.
On $30,000 at 6.53% on the 10-year standard plan ($341.10 a month), total interest is $10,932, about 36% of what you borrowed. Paying $50 extra a month shortens the payoff to 100 months and cuts interest by roughly $2,000. Refinancing to a lower rate or choosing a shorter term reduces it further.