The Starting Number Most Borrowers Never Look Up
Most people who take out a student loan know the amount they are borrowing. Fewer know the interest rate they are borrowing at. Almost nobody calculates the total amount they will repay before signing.
Federal student loan rates are set annually by Congress based on the yield of the 10-year Treasury note from May plus a fixed add-on that depends on the loan type. The rates are fixed for the life of each loan. What you borrow at in your freshman year stays at that rate for the entire repayment period regardless of what rates do afterward.
For loans disbursed July 1 2025 through June 30 2026 per the US Department of Education:
Direct Subsidized Loans for undergraduates: 6.39% fixed.
Direct Unsubsidized Loans for undergraduates: 6.39% fixed.
Direct Unsubsidized Loans for graduate or professional students: 7.94% fixed.
Direct PLUS Loans for parents and graduate students: 8.94% fixed.
One distinction that matters for undergraduates: subsidized loans do not accrue interest while you are enrolled at least half-time. Unsubsidized loans accrue interest from the day they are disbursed — even while you are still in school. Interest that accrues during enrollment capitalizes meaning it is added to the principal balance when repayment begins. A $10,000 unsubsidized loan taken out in freshman year may have a balance of $10,900 or more by the time payments start.
Source: US Department of Education Federal Student Aid 2025-26 interest rate announcement.
What Common Balances Actually Cost to Repay
All examples below use the standard 10-year repayment plan at the 2025–26 undergraduate rate of 6.39%.
Monthly payment formula: P × (r × (1+r)^n) / ((1+r)^n − 1) — Monthly rate r = 0.0639/12 = 0.005325 — n = 120 months for 10-year plan
| Balance | Monthly payment | Total interest | Total repaid |
|---|---|---|---|
| $20,000 | ~$227 | $7,240 | $27,240 |
| $30,000 | ~$340 | $10,800 | $40,800 |
| $50,000 | ~$566 | $17,920 | $67,920 |
| $100,000 (7.94%) | ~$1,210 | $45,200 | $145,200 |
Note: these calculations assume a single loan at a single rate. Most borrowers have multiple loans disbursed across multiple years at different rates. The real calculation requires running the numbers on each loan separately and adding them together. The pattern holds: on a standard 10-year plan you repay approximately $1.36 for every dollar of undergraduate principal at today’s rates.
How Income-Driven Plans Change the Total Cost
Income-driven repayment plans lower monthly payments by extending the repayment period. This is genuinely helpful when income is genuinely low. The trade-off is substantially more total interest paid over the life of the loan.
$30,000 at 6.39% — comparison by plan:
| Plan | Monthly payment | Total interest | Total repaid |
|---|---|---|---|
| Standard 10-year | $340 | $10,800 | $40,800 |
| Extended 20-year | ~$222 | ~$23,280 | ~$53,280 |
The difference: a $118 reduction in monthly payment costs $12,480 in additional lifetime interest — a 115% increase in interest cost to reduce the payment by about 35%.
When income-driven repayment makes sense: When income is genuinely insufficient to cover standard payments in the early career years without hardship. When pursuing Public Service Loan Forgiveness — PSLF requires 10 years of employment with a qualifying government or nonprofit employer while making qualifying income-driven payments. The remaining balance is then forgiven. This can be very valuable for borrowers with high balances and careers in public service.
When income-driven repayment costs you: When you can afford standard payments but choose income-driven for the lower monthly number. The math over time is not favorable unless forgiveness at 20 or 25 years is realistic and the tax implications of forgiven amounts have been considered.
The Opportunity Cost — What Those Payments Could Have Become
There is a cost to student loan payments that does not appear on any statement. It is the investment growth that those dollars would have generated if they had been invested instead of paid to a loan servicer.
The $340 monthly payment on a $30,000 loan over 10 years is not only $40,800 in repayment. It is also $340 per month that cannot go toward a Roth IRA a brokerage account or an emergency fund during the same ten years.
$340 per month invested at 7% average annual return over 10 years grows to approximately $58,800.
At $50,000 in loans the $566 monthly payment over 10 years at 7% would have grown to approximately $98,000.
That is the opportunity cost: not the interest paid but the compound growth foregone on those payments during the repayment window.
This does not mean borrowing for education is wrong. A degree that generates $20,000 more in annual income fully justifies the total cost of a $30,000 loan. The ROI in that case is clear. What changes is how you think about the borrow-versus-save decision at the margin.
The decision about how much to borrow for college is one of the most consequential financial decisions most people make — often before they fully understand personal finance. The true cost is the total repayment plus the opportunity cost of those payments not invested. Running that number before signing — not after — is the only way to make the decision with eyes open.
Calculate your exact student loan payoff timeline and total interest paid on any balance:
Debt Payoff Calculator →Disclaimer: This article is for educational purposes only. Student loan costs depend on loan amounts interest rates repayment plans and individual circumstances. Federal loan rates change annually. Consult studentaid.gov for the most current rate information and a qualified financial advisor for guidance specific to your situation. The opportunity cost calculations shown assume historical average returns and do not predict future investment results.