Loan Details
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Enter your loan details and click Calculate to see your payment schedule.
How Student Loan Payments Are Calculated
The math behind your monthly payment, and what actually changes your total cost
The payment formula
Student loan payments use the standard amortization formula: Payment = P × (r × (1+r)ⁿ) / ((1+r)ⁿ − 1), where P is your principal balance, r is your monthly interest rate (annual rate ÷ 12), and n is the total number of monthly payments. This is the same formula banks use for mortgages and auto loans — it produces a fixed payment where more of each payment goes toward principal (and less toward interest) as your balance shrinks over time. That's exactly what the amortization table above shows month by month.
Fixed vs. variable rate
Federal student loans (subsidized, unsubsidized, and PLUS) are fixed-rate for the life of the loan — the rate is set once a year, on July 1, based on the 10-year Treasury note auction, and never changes for loans disbursed in that period. Private student loans can be fixed or variable. A variable rate is usually lower at the start but can rise — sometimes substantially — over a 10-20 year term, so a lower initial variable rate is not automatically the cheaper option once you project the full repayment period. If you're comparing a fixed federal rate against a variable private offer, run both through this calculator at a stress-tested higher rate (add 2-3 percentage points to the variable offer) before assuming the private loan wins.
Capitalized interest — the cost that hides until repayment starts
Interest on unsubsidized federal loans and most private loans accrues from the day the loan disburses — including while you're still in school. Interest on subsidized federal loans does not accrue during school or the grace period; the federal government covers it. When repayment begins, any interest that built up during school or a deferment is typically capitalized — added to your principal balance — so you then pay interest on that added amount too.
| Unsubsidized loan principal | $27,000 |
| Interest accrued over ~4 years in school (at 6.53%) | ≈ $7,050 |
| Balance at capitalization (repayment start) | ≈ $34,050 |
| Extra lifetime interest this capitalized amount adds | Use the "Capitalized Interest" field above ↑ |
Use the Capitalized Interest at Repayment Start field in the calculator above to see exactly how much this adds to your total cost — enter your estimated accrued interest and recalculate. It's often a bigger number than borrowers expect, which is why some borrowers choose to make small interest-only payments while in school specifically to avoid capitalization.
Reading your amortization schedule
Early payments
Skew heavily toward interest. On a 10-year loan, roughly the first 2-3 years pay down proportionally little principal — this is normal amortization math, not a sign anything is wrong.
"Paid Off" column
Shows the percentage of your original balance you've retired. Use it to see how extra payments accelerate progress compared to the standard schedule.
Yearly Summary view
Switch the amortization table to "Yearly Summary" to see annual totals instead of 120+ monthly rows — useful for a quick gut-check on any given year.
Export CSV
Download your full schedule to a spreadsheet if you want to model your own scenarios (e.g., a raise in year 3) beyond what the extra-payment field supports.
Extra payments and prepayment
Federal student loans have no prepayment penalty. Extra payments (or a one-time lump sum) go entirely to principal once you tell your servicer to apply them that way — otherwise some servicers apply extra amounts to future scheduled payments instead of reducing principal, which saves far less interest. The "Extra Payment Savings" panel above models the interest saved and months shaved off assuming extra payments are applied directly to principal every month.