Interest Savings Calculator (USA)
See exactly how much interest you'd save with extra monthly payments, a lump sum, biweekly payments, an annual bonus payment, or a lower rate — plus how many years earlier your loan would be paid off.
| # | Date | Payment | Principal | Interest | Balance |
|---|---|---|---|---|---|
| Calculate to see schedule | |||||
How to use the interest savings calculator
Four quick steps show how much interest a payoff plan saves — from extra payments, a lump sum, biweekly billing, or a lower rate — plus how many years earlier the loan clears, with a full amortization schedule and a downloadable PDF.
Enter your current loan
Your balance, interest rate, and the years still left on the term.
Choose a payoff strategy
Extra each month, a yearly bonus payment, a lump sum today, or biweekly payments.
Add a rate or term change
Optional — model a refinance or recast, and include the costs to switch.
Read results & save a PDF
See interest saved, time saved, your debt-free date, and a full schedule.
How interest savings are calculated
Interest is charged on your balance every month, so anything that shrinks the balance shrinks every charge that follows. The calculator builds two amortization schedules — one for your loan as it stands, one for your plan — and takes the difference. Here is the exact math.
Worked example — a 350,000 balance at 6.75% with 30 years left, plus 200 a month
Monthly P&I: ≈ 2,270
Interest with no changes: 2,270 × 360 − 350,000 ≈ 467,300
With 200 extra: loan clears in ≈ 285 months (23 yrs 9 mo)
Interest with the plan: ≈ 352,300
≈ 115,000 of interest saved and 6 yrs 3 mo off the term — for about 57,000 of extra payments, or 2.02 saved per extra 1 paid.
Interest savings charts
Handy lookups for the questions people ask most — what extra payments do, what a lower rate does, how the strategies compare, and why timing matters. Figures use a 350,000 balance at 6.75% with 30 years remaining and a monthly P&I of about 2,270, unless noted.
| Extra / month | Payoff time | Total interest | Interest saved | Time saved |
|---|---|---|---|---|
| None | 30 yrs | 467,300 | — | — |
| 100 | 26 yrs 5 mo | 400,100 | 67,200 | 3 yrs 7 mo |
| 200 | 23 yrs 9 mo | 352,300 | 115,000 | 6 yrs 3 mo |
| 300 | 21 yrs 7 mo | 315,400 | 151,900 | 8 yrs 5 mo |
| 400 | 19 yrs 11 mo | 286,300 | 181,000 | 10 yrs 1 mo |
| 500 | 18 yrs 6 mo | 262,500 | 204,800 | 11 yrs 6 mo |
The savings curve is steep at the start: the first 100 a month does the most work per dollar, because it is doing that work for the longest. Figures assume every extra dollar is applied to principal immediately.
| Rate | Monthly P&I | Total interest | Interest saved |
|---|---|---|---|
| 6.75% | 2,270 | 467,300 | — |
| 6.25% | 2,155 | 425,800 | 41,500 |
| 5.75% | 2,042 | 385,200 | 82,100 |
| 4.75% | 1,826 | 307,300 | 160,000 |
Roughly 41,000 of interest saved per half point on this loan, before closing costs. Enter your costs to switch in the calculator to see net savings rather than gross.
| Strategy | Interest saved | What it costs you |
|---|---|---|
| 200 extra a month | ~115,000 | 200 more each month, no fees |
| Biweekly payments | ~110,700 | One extra payment a year |
| 10,000 lump sum today | ~59,500 | 10,000 now, same payment after |
| Refinance to 5.75% | ~82,100 | Closing costs, new 30-year clock |
| Switch to a 15-year term | ~259,800 | About 827 more each month |
Biweekly billing is close to paying about 189 extra a month, so check whether your servicer charges a setup fee for it — sending the extra yourself is usually free. Lump-sum figures assume you keep the original payment after the payment drops.
| Paid in | Interest saved | Time saved |
|---|---|---|
| Year 1 | ~59,500 | 2 yrs 7 mo |
| Year 5 | ~43,700 | 2 yrs 1 mo |
| Year 10 | ~29,600 | 1 yr 7 mo |
| Year 20 | ~9,700 | 9 mo |
An identical payment is worth several times more early in the loan, because it removes interest for every month that remains. Amounts are illustrative and rounded.
balance drops faster
charges shrink
years come off
Interest is rent on the balance you still owe. Cut the balance and you cut every future interest charge, which pulls the payoff date closer.
- Extra principal — applied in full to the balance, not spread across the payment.
- Lower interest — a smaller balance means a smaller charge next month, and every month after.
- Shorter term — with more of each payment going to principal, the loan reaches zero years early.
Everything the calculator works out
One set of loan details and one payoff plan gives you the full picture — the interest saved, the time saved, and the schedule behind both.
Key figures behind interest savings
Built for any payoff question
Whether you are rounding up your payment, deciding what to do with a bonus, or weighing a refinance, the same calculator prices the decision in interest and years.
Wants to add a comfortable amount to every payment and see what that habit is worth over the life of the loan.
- Try a few amounts side by side
- Start with what you can sustain
- Check the return per extra dollar
Has a tax refund, bonus, or one-off sum and wants to know what putting it against the mortgage actually buys.
- Model it as a lump sum today
- Or set it as a yearly payment
- Keep an emergency fund first
Comparing a lower rate or a shorter term against simply paying extra, and wants the numbers net of closing costs.
- Enter the new rate and term
- Add your costs to switch
- Read the net savings line
7 tips for saving mortgage interest
A few habits make a payoff plan work harder — and keep the projection honest.
Interest savings calculator FAQ
The strategy, timing, refinance, and servicer questions people ask most about paying a mortgage down early.
It depends on your balance, rate, and how much extra you pay, but the effect is usually larger than people expect. On a 350,000 loan at 6.75% over 30 years, an extra 200 a month cuts total interest from about 467,300 to about 352,300 — roughly 115,000 saved — and pays the loan off about 6 years 3 months sooner.
Every extra dollar goes straight to principal, so it removes all the future interest that dollar would have carried for the rest of the term. That is why small, early, consistent extra payments do so much work.
Mortgage interest is charged on the balance each month, so anything that shrinks the balance shrinks every interest charge that follows. A regular payment only reduces principal by a small slice in the early years, while an extra payment reduces it dollar for dollar.
Because the saving compounds across the remaining term, an extra payment made in year 2 saves far more than the same payment made in year 20. Timing matters as much as amount.
A lump sum paid today saves the most per dollar, because it removes principal at the earliest possible moment. Steady monthly extras usually save more in total, though, simply because they add up to far more money over the life of the loan.
Most people get the best result by combining both: a lump sum from a bonus or tax refund plus a modest monthly amount they can sustain. The calculator lets you model each separately or together.
Paying half your mortgage payment every two weeks produces 26 half payments a year, which equals 13 full payments instead of 12. That extra payment goes to principal and shortens the loan.
On a 350,000 loan at 6.75%, biweekly payments save roughly 110,700 in interest and about 6 years — similar to paying about 189 extra a month. The calculator models it as one extra payment spread evenly across the year.
They solve different problems. A lower rate reduces the cost of every future dollar of debt and usually lowers your payment, while extra payments reduce how long you carry the debt at all. Refinancing has closing costs; extra payments have none.
Dropping from 6.75% to 5.75% on a 350,000 loan saves about 82,100 in interest, while 200 a month extra saves about 115,000. Doing both is stronger than either alone, which is why the calculator lets you set a new rate and extra payments at the same time.
Most US mortgages written today have no prepayment penalty, but some loans do, and rules vary by lender, loan type, and state. Penalties are more common on non-qualified, investor, and some older loans, and often apply only in the first few years.
Check your note or ask your servicer before you start a payoff plan. This calculator assumes no penalty applies, so a penalty would reduce the savings shown.
Paying down a mortgage is a guaranteed return equal to your interest rate, with no market risk. Investing may return more over long periods, but the return is uncertain and can be negative.
The honest comparison is your mortgage rate against a realistic after-tax return at a risk level you are comfortable with — alongside emergency savings, employer-matched retirement contributions, higher-rate debt, and how much you value being debt-free. It is a personal decision worth discussing with a qualified financial professional.
Extra money is not automatically applied to principal. Servicers may hold it as a partial payment, apply it to next month’s payment, or put it toward escrow unless you tell them otherwise.
Send the extra as a separate payment marked principal only where possible, check the next statement to confirm the balance dropped by the full amount, and confirm that prepaying does not suspend your normal monthly payment.
General Estimating Notice: This calculator compares two standard amortization schedules using the balance, rate, term, extra payments, lump sum, new rate, and costs you enter. It assumes every extra dollar is applied to principal immediately, that no prepayment penalty applies, and that your rate stays fixed — and it excludes taxes, insurance, escrow, PMI, and servicer fees. Figures are illustrations, not an offer, a quote, or financial advice, and your servicer’s actual handling of prepayments may differ. Confirm prepayment rules, escrow effects, and refinance costs with your servicer or a licensed lender. For planning purposes only.