Student loan payments under a standard repayment plan follow the same amortization math as any other fixed-rate loan — but the typical term length (often 10 years) and typical balance size mean the total interest paid over the life of the loan can end up surprisingly large, even at a moderate rate.
The standard repayment plan spreads your balance evenly across 120 fixed monthly payments (10 years), calculated so the loan is fully paid off with interest included by the final payment. Income-driven repayment plans work completely differently — basing payments on a percentage of discretionary income rather than the loan balance — but the standard plan uses the familiar loan formula.
How the Payment Is Calculated
M = P × [r(1+r)^n] / [(1+r)^n − 1], where P is your loan balance, r is the monthly interest rate (annual rate ÷ 12), and n is the number of payments (120 for a standard 10-year term). The same formula that determines a mortgage or auto loan payment applies here — only the typical balance and rate differ.
A Worked Example
On a $30,000 balance at 5.5% over the standard 10-year term, the monthly payment comes out to about $326. Over the full 120 payments, total repayment is roughly $39,100 — meaning $9,100 in total interest on top of the original balance, or about 30% extra. Extending to a 20-year term (available under some repayment plans) would lower the monthly payment to around $206, but nearly double total interest paid to about $19,400, since the balance accrues interest for twice as long.
Common Mistakes to Avoid
- Assuming the standard plan is always best: income-driven plans can lower payments significantly for lower earners, but often extend the payoff timeline and can increase total interest paid — the right choice depends on your income trajectory.
- Not making payments during a grace period if you can afford to: interest often still accrues during deferment or grace periods on unsubsidized loans — early payments can meaningfully reduce eventual total cost.
- Ignoring loan forgiveness program eligibility: certain careers (public service, teaching) may qualify for forgiveness programs that change the payoff math entirely.
- Refinancing federal loans into private ones without checking what's lost: federal loans carry protections (income-driven plans, forgiveness eligibility, deferment options) that private refinancing typically eliminates.
Bottom Line
Standard student loan repayment uses the exact same math as any amortized loan, just usually over a longer, fixed 10-year term. Use a Student Loan Calculator to see your monthly payment and total interest under the standard plan for your actual balance and rate.