What this shows, and what it cannot
Student debt is unusual: the amount is fixed long before you have any income, the rate was set by the year you borrowed rather than by you, and there are repayment routes that have nothing to do with the size of the balance. This calculator handles the straightforward case — a fixed rate paid off in equal monthly instalments — which is the standard plan and most private loans.
It cannot model an income-driven plan, forgiveness after a set number of qualifying payments, a graduated plan whose payment rises over time, or periods of deferment while interest keeps accruing. Those depend on your earnings and on rules that change, so a number here would look authoritative and be wrong. Use this for the shape of the debt, and your servicer for what you actually owe next month.
What a typical balance costs
$30,000 at 6.5%, the example above:
| Plan | Monthly payment | Total interest |
|---|---|---|
| 10 years | $340.64 | $10,877.41 |
| 10 years, plus $50 a month | $390.64 | $8,892.29 |
| 20 years | $223.67 | $23,681.74 |
The middle row is the interesting one. Fifty dollars a month — less than the gap between the ten and twenty year payments — ends the loan 20 months early and saves nearly $2,000.
If you hold several loans
Work out each one separately, then decide where a spare dollar goes. Sending everything extra to the highest rate first costs the least overall. Clearing the smallest balance first costs slightly more but removes a payment from your life sooner, which some people find easier to keep up. Both beat spreading it evenly. Whichever you pick, tell the servicer in writing that extra money is for the principal of a specific loan.
Before refinancing a federal loan
Refinancing to a lower rate is straightforward arithmetic, and you can check it above by entering the new rate and term. What the arithmetic will not show you is what you give up: refinancing a federal loan with a private lender ends access to income-driven plans, forgiveness programmes and federal deferment. That can be a fair trade for a much lower rate, or a bad one if your income is uncertain. Read what you are giving up before you compare payments.