How Student Loans Are Calculated: Interest Before You Ever Make a Payment

Most loans start costing you money when you start repaying them. A student loan — if it is unsubsidized — starts costing you money the day the money lands, years before the first bill. By graduation, thousands of dollars of interest can be sitting on top of what you borrowed, and at that moment the loan quietly changes size. This is the mechanics of how student loans are calculated: where the interest comes from, when it compounds, and what the standard repayment does with the result. The figures are federal Direct Loan figures for the 2026-27 year, labelled as such; private loans follow similar mechanics with their own rates.

Two federal flavours

Subsidized loans (need-based, for undergraduates): the government pays the interest while you are enrolled at least half-time, during the six-month grace period after you leave school, and during deferment. The balance you graduate with is the balance you borrowed — it stays flat.

Unsubsidized loans — and PLUS loans, and nearly all private loans: interest accrues from the day of disbursement and it is entirely yours. Nothing is billed while you are in school, which is exactly why the accrual goes unnoticed: it piles up silently, in the background, for years.

The rates, with the year on them

For loans first disbursed in 2026-27, federal Direct Loans are fixed for the life of each loan at 6.52% for undergraduates, 8.07% for graduate unsubsidized loans and 9.07% for PLUS loans. The rates are set by law each year — not negotiated, and not based on your credit. And each year's borrowing is its own loan at its own rate: a four-year degree can mean four separate loans at four different fixed rates, which is why our Student Loan Calculator stacks up to five loans at their own rates rather than pretending a degree is one loan.

Accrual in school: the pile, year by year

While you make no payments, the interest is simple — it does not compound in school. But simple interest on a growing stack still grows, because each new year's borrowing joins the pile. Take an unsubsidized borrower who takes $5,000 at the start of each of four school years, all at 6.52%, and pays nothing:

Borrowed: $20,000. Interest accrued in school: $3,479.57. Balance at graduation: $23,479.57. Put it monthly and it feels smaller than it is: the first $5,000 alone accrues $27.17 a month — a subscription you never signed up for, running from freshman year.

Capitalization: the moment the loan changes size

When repayment begins — and again at the end of a deferment or forbearance — the unpaid interest is capitalized: added to the principal. From that day forward you pay interest on the interest. The $23,479.57, not the $20,000 borrowed, becomes the principal that repayment is calculated on. Capitalization is the hinge of the whole system: before it, interest is a pile beside the loan; after it, the pile is part of the loan, generating interest of its own for a decade.

Repayment: ten years of ordinary amortization

The standard plan repays the capitalized balance over 10 years — 120 payments of ordinary amortization. On $23,479.57 at 6.52% that is $266.84 a month, $32,021.37 in total, of which $8,541.80 is repayment-phase interest. Add the in-school accrual and the lifetime interest on $20,000 of borrowing comes to $12,021.37 — interest equal to 60% of what was borrowed, on a loan most borrowers think of as "the cheap kind". The Loan Calculator handles any single loan in this stack in any direction, if you want to check one year's borrowing on its own.

The in-school interest option, priced

You are allowed to pay the interest while in school — nothing about the loan requires waiting for the bill. On this example, paying the $3,479.57 as it accrues keeps principal at the original $20,000. Repayment then runs at $227.30 a month with $7,275.94 of repayment interest; combined with the interest paid along the way, total interest is $10,755.52. Against $12,021.37, capitalization's price on this loan is $1,265.86. Whether that trade suits a given student is a budget question, not a rule — but it should be made with the price tag showing, and the price tag is $1,265.86 on every $20,000 borrowed this way at this rate. Households juggling this alongside ordinary debts can model the non-student side in the Debt Payoff Calculator.

The fine print that moves real bills

Two last mechanics. First, the loan fee: for 2026-27 Direct subsidized and unsubsidized loans, a fee of 1.057% is deducted before disbursement. A $20,000 loan therefore delivers $19,788.60 — and you repay the full $20,000. The missing $211.40 was never in your account, but it is in your balance. Second, the limit of every calculator including ours: federal loans carry income-driven repayment plans and forgiveness programs that no amortization math can weigh, because they depend on your future income and employment. Before prepaying a federal loan aggressively, check those programs at studentaid.gov — the mechanically optimal move is occasionally the wrong one, and only the federal site can tell you.