A student loan has a sticker too: the amount borrowed. And just like a car or a college, that's the smallest the number will ever be. The amount actually repaid depends on the rate, how interest builds up, and how long repayment takes — and the gap between borrowed and repaid is where the real cost hides. Seeing it clearly is the whole point of this lesson.
This is mechanics, not a verdict on whether any particular loan is worth it. It's educational only — not individualized financial advice.
How interest accrues
Interest is the price of borrowing, charged as a percentage of the outstanding balance over time. On a student loan it usually accrues daily on the principal — the amount still owed. The higher the principal and the higher the rate, the faster interest piles up.
The timing is what surprises people. On a subsidized federal loan, the government covers interest while the student is in school, so the balance holds steady until repayment. On an unsubsidized or private loan, interest accrues from the day the money is disbursed — through every semester, every break, and the grace period after graduation. Years of in-school interest can accumulate before a single payment is due.
| Loan type | Interest in school | Effect by graduation |
|---|---|---|
| Subsidized federal | Paid by the government | Balance ≈ amount borrowed |
| Unsubsidized federal | Accrues on the borrower | Balance > amount borrowed |
| Private | Accrues on the borrower | Balance > amount borrowed, often more |
Capitalization: interest that becomes principal
Here's the mechanic that quietly raises the cost the most. While a borrower isn't making payments — in school, during the grace period, or during certain deferments — unpaid interest builds up on the side. At specific moments, that accrued interest is capitalized: added onto the principal. From then on, interest is charged on the new, larger balance — interest on interest.
This is compound interest working against the borrower instead of for them. A small amount of unpaid interest, once folded into the principal, starts generating its own interest. The earlier and more often capitalization happens, the more it costs over the life of the loan.
The real cost over a 10-year term
Most federal loans default to a standard 10-year repayment plan. Stretched over that many years, even a moderate rate adds a substantial amount on top of the principal through amortization — the process where each payment covers that month's interest first, then chips at the principal. Early payments are mostly interest; later ones mostly principal.
| Amount borrowed | Rate | ~Monthly payment | ~Total paid (10 yr) | ~Interest |
|---|---|---|---|---|
| $15,000 | 6% | $167 | $19,980 | $4,980 |
| $30,000 | 6% | $333 | $39,960 | $9,960 |
| $30,000 | 9% | $380 | $45,600 | $15,600 |
| $50,000 | 6% | $555 | $66,600 | $16,600 |
The pattern is steady: the total repaid runs well above the amount borrowed, and both a bigger balance and a higher rate widen the gap. This is the same amortization math behind any loan — the interest, APR & amortization lesson walks it step by step, and the loan payment calculator lets a borrower plug in real numbers.
Borrowing against a likely starting salary
One framing financial educators use to keep total cost in proportion is to weigh borrowing against the likely starting salary of the field a degree leads to. The idea, as a concept, is that a loan balance roughly in line with a first year's expected pay tends to be more manageable on a standard 10-year plan than a balance that dwarfs it — because the monthly payment has to come out of that real income alongside rent, food, and everything else.
This is a way to think about scale, not a rule or a personalized number — actual outcomes vary enormously by field, region, and person, and no one can promise what any degree will pay. The useful move is simply to make the comparison visible: what's being borrowed, against what it's plausibly being borrowed for. Looking up typical starting salaries for a field and lining them up against the projected balance turns an abstract loan into a concrete monthly tradeoff.