See interest saved and time cut off any loan from extra payments.
Project the impact of extra monthly payments or a lump-sum payoff against any consumer loan — mortgage, auto, student, personal. Interest saved, months saved, new payoff date.
Direct answers to the most common questions, in plain language. Skim if you're in a hurry; dig deeper below.
Compare total interest with extra payments vs without.
Interest savings = (total interest on baseline payment schedule) − (total interest with extra payments). Any extra payment goes directly to principal, reducing future interest calculations.
Thousands — sometimes tens of thousands.
On a $300k mortgage at 7%: extra $100/month saves about $40k of interest and 4 years. On a 22% credit card with $5k balance: extra $100 saves $1,500+ and cuts the payoff by years.
Yes — that's the avalanche method.
For maximum interest savings, attack the highest APR first while paying minimums on the rest. Snowball (smallest balance first) gives motivational wins; avalanche gives maximum dollar savings.
Yes for any loan — but check for prepayment penalties.
Most US consumer loans have no prepayment penalties. Some commercial loans, older fixed-rate loans, or specific subprime products do. Check your loan documents before assuming.
The mechanics in short answers — no jargon, no upsell.
Every month, your lender computes interest on whatever you still owe. Lower balance = lower interest charge.
Anything above the scheduled payment goes 100% to principal. The next month's interest calculation uses the new, lower balance.
A principal reduction in year 1 of a 10-year loan saves interest for 9 more years. Earlier extra payments save more than later ones.
See exactly what an extra $50, $100, $500/month — or a one-time $10k lump sum — does to the total cost and payoff date.
Designed so anyone can model their situation in under a minute, with or without a finance background.
Total interest saved by any extra payment.
Years and months cut off the loan.
Mortgage, auto, student, personal — same math.
See impact of one-time large payments.
Interest saved is a risk-free return equal to your loan rate.
Concrete debt-free date after acceleration.
Everything you might ask before, during, or after using this tool.
No — compare to your alternatives. Paying down 22% credit card debt: clear win. Paying down a 3% mortgage when you have a 4% high-yield savings account: skip. The simple rule: pay down debt at higher rates than your investment alternatives can reliably beat after taxes.
Yes — always specify. Otherwise some servicers apply extras to the next scheduled payment (lost interest savings). Write "apply to principal only" on a check or use the principal-only option in online payment.
Usually no — most lenders apply the extra to principal but keep your monthly payment the same and shorten the loan. To reduce your monthly, you usually need to formally recast (small fee) or refinance.
Federal Dodd-Frank rules essentially eliminated prepayment penalties on owner-occupied mortgages. Auto loans: rare. Personal loans: occasional. Student loans (federal): none. Read your loan note before assuming.
Most US consumer loans use simple monthly compounding — interest accrues on balance × monthly rate. Some use daily compounding (slightly higher effective rate). The math here approximates monthly; effect of method is small for typical loans.
Mortgage interest is deductible if you itemize — by paying extra, you reduce interest paid and therefore the deduction. Math: even after losing the deduction, savings are positive at typical rates and tax brackets. The deduction softens the win, doesn't eliminate it.
Depends on the certainty of the investment return. Paying down a 7% loan is a guaranteed 7% return. To beat it, your investment expected after-tax return needs to be meaningfully higher. For most investors, paying down high-rate debt is the better risk-adjusted choice.
Yes — and earlier is dramatically better. A $10,000 lump sum applied to a 7% mortgage in year 2 saves more than the same amount applied in year 15. Time-since-application is the multiplier.
Other Lazysmirk tools that pair well with this one.
See how extra EMI payments, yearly prepayments, and lump-sum part payments reduce your home loan tenure and save thousands in interest.
See how monthly extras, bi-weekly payments, and yearly lump sums shorten your mortgage and save thousands in interest.
See the full month-by-month amortization schedule for any loan — EMI, principal vs interest split, and total interest paid. Works for home, car, personal, and student loans.
See how fast you can become debt-free with the snowball method — pay off your smallest debt first, then roll the payments forward. Compare snowball vs avalanche side by side.
See how long minimums take to pay off, and how much faster + cheaper a fixed payment finishes the debt.
Interest = remaining balance × monthly rate. Every dollar of balance you eliminate is a dollar that won't generate interest for the rest of the loan.
Pay $1 of extra principal in month 1 of a 30-year loan at 7% = save about $6 of interest over the loan life.
Pay that same $1 in month 200 = save maybe $0.50. Time is the multiplier.
Paying down a 7% loan is mathematically equivalent to a 7% guaranteed, risk-free investment.
In a world where Treasury yields are 4–5%, and equities have 7% expected return with massive variance, a guaranteed 7% from debt paydown is excellent.
The higher the loan rate, the more obvious the choice.
Highest rate first (avalanche): saves the most dollars.
Smallest balance first (snowball): motivational wins faster.
In practice, the dollar difference is usually small ($100–500). Pick whichever you'll actually finish.
1. Emergency fund (3–6 months).
2. 401(k) match (free money — don't skip).
3. High-rate debt (anything 8%+).
4. Max IRA / HSA.
5. Lower-rate debt extras.
6. Taxable investing.
Most "pay extra on mortgage" mistakes happen when steps 1–4 aren't done first.
Two short notes worth reading before you trust any number on this page.
Your loan amount, rate, and prepayment inputs never leave your device. No accounts, no cookies on your numbers, no analytics on the values you type. Disconnect from the internet and it still works.
We are not a bank, NBFC, advisor, broker, or distributor of any financial product. The numbers shown here are estimates for educational purposes only, based on the inputs you provide.
Results are not financial, legal, or tax advice. Please consult a qualified professional before any decision about your loan, investments, or personal finances. Actual loan terms and charges depend on your bank and individual circumstances.
