Federal vs private: why this calculator covers both
Federal loans are simple: a fixed interest rate, a 10-year standard repayment term, and daily-interest accrual. Private loans are whatever your lender decided they should be — variable or fixed, 5 to 20 years, sometimes with origination fees baked in. From a math perspective, though, both behave like any other installment loan: balance, APR, term, payment. The calculator above treats them the same way.
A real example: Priya's $41,000 in loans
Priya graduated with $41,000 in federal student loan debt — $28,000 in unsubsidized undergraduate loans at 6.54% and $13,000 in grad PLUS loans at 8.05%. She's not on a forgiveness track. Her standard 10-year payment is about $465/month. Here's what adding extra payment does:
- Standard ($465/month): Paid off in 10 years. Total interest: $14,800.
- $600/month (+$135): Paid off in 7.5 years. Total interest: $10,600. Saves $4,200.
- $800/month (+$335): Paid off in 5.5 years. Total interest: $7,400. Saves $7,400.
- $1,000/month (+$535): Paid off in 4 years. Total interest: $5,600. Saves $9,200.
The jump from $465 to $600/month costs Priya $1,620/year in extra payments, but saves her $4,200 in interest and returns 2.5 years of her life. That's a strong return.
How to use this calculator
- Find your loan details: Log into StudentAid.gov for federal loan balances, interest rates, and servicer information. For private loans, check your lender's portal. If you have multiple loans, use the combined balance and a weighted-average interest rate.
- Confirm you're not on a forgiveness track: If you're in PSLF (Public Service Loan Forgiveness) or an IDR plan aimed at forgiveness at year 20/25, extra payments are often counterproductive — they reduce the balance that would have been forgiven.
- Enter your current or planned payment: Start with your standard payment, then increase it to see the impact. The calculator shows payoff date, total interest, and months saved.
- Direct extra payments to the highest-rate loan: If you have multiple loans at different rates, pay the minimum on the lower-rate ones and pile extra payments on the highest-rate loan. Federal servicers generally let you specify which loan receives additional payment.
The "just pay the minimum" question
If you are on track for Public Service Loan Forgiveness (PSLF), an income-driven plan with forgiveness at year 20/25, or you work in a field with state-level repayment assistance — do not prepay your federal loans. Every extra dollar is a dollar you lose to forgiveness. This calculator is for people who are paying off their loans, not waiting them out.
If you are not on a forgiveness track, the math is usually clear: federal unsubsidized loans for grad school run 7–9% APR, which is higher than most mortgages and roughly even with a diversified stock portfolio's historical return. Paying them down is a guaranteed, tax-free return at that rate. For most households, that's a strong risk-adjusted investment.
Why extra $100/month matters so much
On a $34,000 loan at 6.53% over 10 years, the standard payment is ~$386. Adding just $100 extra per month cuts the payoff by roughly two years and saves about $2,500 in interest. Adding $200 extra — a meal-kit subscription and two streaming services — saves over $4,000 and knocks more than three years off the clock.
The effect compounds because student loan interest accrues daily. Every extra dollar applied to principal reduces the daily interest charge for every subsequent day of the loan. Paying $100 extra in month 3 is more valuable than paying $100 extra in month 80, because it reduces interest for all the months in between.
Refinance vs repay
Refinancing a federal loan into a private one permanently gives up income-driven repayment, PSLF, and the deferment/forbearance options that federal borrowers get. That is a massive safety net to walk away from — even if your private rate is 2% lower. The rule of thumb: only refinance federal loans if your income is high, stable, and you would pay the loan off inside 5 years anyway. For private loans with no such safety net, refinancing is a pure rate shopping exercise.
Where student loans sit in your payoff order
Student loans are usually the lowest-APR debt in your portfolio — lower than credit cards (definitely), lower than auto loans (usually), and sometimes tied with a mortgage. Under the avalanche strategy, this means they often get paid last. That is usually correct — clear the 22% credit card before the 6.5% student loan, not the other way around.
Tax deduction: real but capped
You can deduct up to $2,500 of student loan interest per year on your federal taxes, subject to income limits (~$95K single / $200K married for the full deduction as of recent tax years). That is a useful offset — but it shrinks as your income grows, and it is just a deduction, not a credit. Do not let the tax deduction keep you in debt longer than necessary; the interest itself is more expensive than the deduction is worth.
Frequently asked questions
I have 8 different federal loans at different rates. How do I use this calculator?
Use the weighted average: multiply each loan's balance by its rate, add them all up, and divide by total balance. Enter that weighted-average rate. Then plan to direct all extra payments to your highest-rate loan specifically (StudentAid.gov lets you designate which loan receives extra payment). This calculator gives you the total-loan timeline; the actual payoff sequence matters for which specific loan you attack first.
Should I pay extra on student loans or max my Roth IRA?
If your student loan rate is above 7–8%, debt payoff has the edge in expected returns (guaranteed vs probabilistic). Below 5–6%, the Roth IRA wins for most young investors — the tax-free growth over 30+ years is hard to replicate. In the 6–7% zone, this is a close call that depends on your risk tolerance and the specific loans. At a minimum, always contribute enough to any employer 401(k) match before paying extra on loans.
My income-driven repayment payment is $0 right now. Should I still pay?
If you're pursuing PSLF or an IDR forgiveness plan: do not voluntarily pay more than required. Paying extra reduces the forgiveness you'll receive. If interest is accruing while you pay $0, that accrued interest is typically forgiven along with the principal at the end of the repayment period. Focus on keeping your income documented and staying on the IDR plan.
What happens if I pay more than the statement shows as "amount due"?
Most federal servicers automatically apply overpayments to the lowest-interest loan, which is usually not what you want. To direct extra payments to a specific loan, you typically need to call your servicer or use their online portal to specify allocation. Document this in writing — servicers occasionally misapply payments. Check your loan balances the following month to confirm the payment landed where you intended.
My private loan has a variable rate. How do I plan around that?
Enter your current rate and note when it adjusts (usually annually, tied to SOFR or LIBOR successor indices). If rates are rising, the case for accelerated payoff or refinancing to a fixed rate gets stronger. If rates are stable or falling, your current plan may be fine. Revisit this calculator whenever your rate adjusts. For peace of mind, refinancing a variable-rate private loan to a fixed rate through a credit union or SoFi is worth exploring if your credit has improved since origination.
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For education only. Not financial advice.