How it works
An extra principal payment is money applied beyond your required installment that retires balance directly — and because student loan interest computes on the outstanding balance, every dollar removed early stops accruing for the rest of the loan's life. That feedback loop is why small extras punch far above their weight: adding $75 a month to a $31,500 balance at 5.4% cuts the total interest bill by more than $1,600 and pulls the payoff date forward by twenty months, without renegotiating anything with anyone. The calculator amortizes your loan twice — once at the required payment, once with the extra — and reports the gap in interest, months, and final totals. Two mechanics decide whether theory becomes reality. Application direction: servicers must be told (or confirmed) to apply surplus to principal rather than as an advance on next month's installment, which saves almost nothing. Persistence: the savings compound with time, so an extra sustained for five years beats the same dollars scattered. The yearly table shows the payoff path with the extra running, and the stacked chart splits every dollar spent into principal retired versus interest burned — watching the principal share accelerate in later years is the whole argument in one picture.
Formula
New payoff amortizes at (payment + extra); interest saved = baseline total interest − accelerated total interest
Tips
- Confirm the servicer applies extras to principal, not as a future-payment advance.
- Automate the extra on payday — sporadic round numbers rarely survive contact with life.
- Point the extra at the highest-rate loan first if you carry several.
- At typical rates, prepayment is a guaranteed return matching your loan APR — compare before investing spare cash.
- Keep one month of expenses liquid before accelerating any debt payoff.
Frequently asked questions
- Do extra payments on student loans save interest?
- Yes, dollar-for-dollar against future accrual. An extra $75 monthly on a $31,500 balance at 5.4% removes about $1,700 of interest and shortens payoff by twenty months, because the prepaid principal never generates another day of interest. The earlier the extras start, the larger the compounding saving.
- How much faster can I pay off my student loans?
- It scales with the extra relative to the balance. Roughly $75 extra per month on these defaults trims about twenty months; doubling to $150 roughly doubles the effect. The calculator converts any amount into exact months saved on your specific balance, rate and current payment.
- Why didn't my extra payment reduce my balance?
- Most servicers apply surplus as an advance on the next installment unless instructed otherwise — the balance stays untouched and the due date moves. Request principal-only application in writing or via the portal setting; that single instruction is where the savings live.
- Is it better to pay off student loans or invest?
- Compare rates honestly: prepaying a 6.8% loan is a guaranteed, tax-free 6.8% return, while investments are uncertain and taxable. Common guidance puts high-rate loans ahead of investing and low-rate loans alongside it — the calculator supplies the guaranteed side of that comparison.
- Can I make extra payments without penalty?
- Federal student loans carry no prepayment penalties, and private loans overwhelmingly dropped them too. Check the promissory note for older private paper, then automate the extra — the absence of penalties means the only cost of trying is the cash flow itself.