About the Student Loan Calculator
Student loans are usually 10-year standard amortizing loans — the same math as a mortgage in miniature — with material differences: no collateral, sometimes factory interest-subsidy rules while in school, and a federal government framework offering income-driven options, deferment and Public Service Loan Forgiveness that private lenders do not match.
Use this tool to price your standard repayment and, knowing your circumstances are stable, to see what extra principal removes in both time and interest.
The formula behind it
The standard fixed-payment formula drives the schedule:
M = P × r × (1+r)^n / ((1+r)^n − 1)P = balance, r = APR/12, n = 12×years. Interest accrues daily in practice; at the quoted APR, total interest = M×n − P for standard plans. Voluntary extras apply directly to principal (the accelerated schedule simulated here).
Worked example
Defaults — $32,000 at 5.8% over a standard 10-year plan:
- Standard payment ≈ $352.06 per month for 120 months.
- Total paid ≈ $42,247, meaning $10,247 of interest on a $32,000 loan.
- Raise the extra field to $100 per month (default is $50): payoff drops to about 87 months and interest falls to roughly $7,260.
Takeaway: One extra $100 payment monthly erases ~33 months and ~$2,990 of interest — a 29% discount on the original finance charge.
What moves the result
- Subsidized vs unsubsidized — subsidized federal loans do not accrue interest while in school; unsubsidized ones accumulate interest from disbursement day.
- Repayment plan — Standard builds equity fastest; income-driven plans can stretch to 20 or 25 years.
- Consolidation — averaging several federal loans’ rates can raise total interest versus keeping lowest-rate loans on separate autopays.
- Prepayment — voluntarily applied principal (automatic once your payment clears) directly lowers total interest.
Practical tips
- Enroll in autopay for the 0.25-point servicer discount before considering prepayments — it is free money on every remaining month.
- If you are shooting for PSLF or on an income-driven plan, extra principal may be wasted effort — the forgiveness rules, not speed, set your outcome. Price your plan cases carefully.
- For multiple private loans, target the highest-rate loan with extras (snowball method for morale, avalanche for pure dollars).
- Unpaid interest while in school capitalizes at repayment’s start — even small payments during school beat waiting.
- Anything beyond the minimum payment on federal loans should come after securing a proper emergency fund.
Frequently asked questions
What if I can’t afford the standard payment?
Federal borrowers should check income-driven plans (IBR, PAYE, REPAYE/SAVE) which cap payments as a share of discretionary income. Private loans depend entirely on the lender’s forbearance terms.
Do either subsidized federal loans give you a grace period after graduation?
Most offer roughly 6 months after separation before repayment begins; interest rules differ by loan subtype.
Is refinancing federal loans risky?
Yes — refinancing with a private lender permanently strips borrower benefits such as income-driven options and forbearances. Only do it for a rate gap that outweighs every benefit you keep.