What this calculator does
Enter a loan amount, an interest rate, and a term, and the calculator derives the fixed monthly payment using the standard amortizing-loan formula, then builds the full month-by-month schedule: how each payment splits between interest and principal, how the balance falls, and exactly when the loan is paid off. Add an optional home value and it estimates when your balance reaches 80% of that value — the point at which you can generally request PMI cancellation under the federal Homeowners Protection Act.
The extra-payment field is one of the most useful parts of the tool. Add even a small monthly extra and watch the payoff date and total interest change. The calculator rebuilds the entire schedule in real time, so you can see not just that extra payments help, but by exactly how much and exactly when.
What the inputs mean
- Loan amount — the principal you are borrowing, not the purchase price. If you are putting 10% down on a $450,000 home, the loan amount is $405,000.
- Interest rate, annual — the note rate on your loan, not the APR. The note rate is the one used to compute your payment; the APR folds in fees and is always higher. Enter the note rate here.
- Loan term — standard options are 30 years (360 months) and 15 years (180 months). The calculator accepts any whole number, so a 20-year or 10-year loan works too.
- First payment date — the date of your first scheduled payment, used to date the schedule. Mortgage payments are paid in arrears, so your first payment is typically one full month after closing.
- Home value — optional. Used only to estimate PMI removal. Leave it blank if you have no mortgage insurance or if you already know you put 20% or more down.
- Extra payment, each month — an additional principal payment applied every month on top of the required payment. It goes straight to principal, so every dollar here reduces the balance on which next month's interest accrues.
What the outputs mean
- Monthly payment — principal and interest only. It does not include property taxes, homeowners insurance, mortgage insurance premiums, or HOA dues. Your actual monthly outlay will be higher once those are added to your escrow payment.
- Total interest cost — the total of every interest dollar you will pay over the full term. On a $400,000 loan at 6.5% over 30 years this is $510,177 — more than the original loan itself. This is the number most lenders do not volunteer.
- Interest saved — visible only when you enter an extra payment. This is the difference between total interest on the standard schedule and total interest on the accelerated one. It is computed by building both schedules in full, not approximated.
- Crossover month — the month in which cumulative principal paid to date first exceeds cumulative interest paid to date. On a 30-year loan at 6.5% this is typically around month 216 (year 18). Before that point, more of every dollar you have paid has gone to the lender than to your equity.
- PMI removal, est. — the month the scheduled balance first reaches 80% of the home value you entered. This is an estimate of when you could request cancellation under the Homeowners Protection Act, not a guarantee. See the PMI guide for the full rules.
Loan entry
Used only to estimate when you reach 20% equity and can request PMI removal.
Applied straight to principal, every period.
Ledger reads
Paid in full$0
per month, principal & interest
- Payoff date
- —
- Time saved
- —
- Total of payments
- $0
- Total interest cost
- $0
- Interest saved
- —
- PMI removal, est.
- —
Where the money goes
Cumulative principal crosses cumulative interest at month —.
Full schedule
Every month is listed, grouped by annual period — click a year to open or close it. Add a one‑time extra principal payment to any month in the extra column, and every month after it recalculates automatically: lower balances, less interest, an earlier payoff.
| Date | Period | Payment | Principal | Interest | Extra | Balance |
|---|
What an extra payment buys you
Three versions of the same loan, side by side — no extra payments, and two monthly extra amounts you can change (click the dollar figures in the header). Scenarios use the loan entries above and ignore any one-time extras typed into the schedule, so it's a clean comparison.
| Standard schedule | +$ / mo | +$ / mo |
|---|
How the numbers work
Your monthly payment here covers principal and interest only — the two parts of a mortgage that follow strict math. It doesn't include property taxes, homeowner's insurance, PMI, or HOA dues, since those vary by lender, location, and policy. Ask your lender for the full PITI figure before you budget against this number.
Early in a loan, most of each payment goes to interest, because interest is charged on whatever balance is still outstanding, and the balance starts at its highest point. As the balance shrinks, less of each payment is eaten by interest and more goes to principal — that's the "crossover" the chart marks: the month your payments start doing more work for you than for the lender.
Extra payments shrink the balance directly, which means every payment after an extra one is calculated against a smaller number — so it compounds. A single early lump sum often saves more in total interest than the same amount spread thin over many months, simply because it starts working sooner.
Is this the same as what my lender will quote me?
It's a close estimate for a standard fixed-rate loan compounded monthly. Lenders may round differently, add fees, or quote APR instead of the note rate — treat this as planning, not a binding number.
Does it handle adjustable-rate mortgages (ARMs)?
No — this calculator assumes one fixed rate for the full term. For an ARM, you'd need to re-run the numbers with the new rate each time it adjusts.
What happens to the "extra payment" numbers if I change the loan amount or rate?
One-time extra payments you've entered in the table stay in place by period number. If you want a clean slate, use "Clear extra payments" above the schedule.
How is mortgage interest calculated each month?
Multiply your remaining balance by your annual rate divided by 12. On a $400,000 balance at 6.5%, that's $400,000 × 0.065 ÷ 12 = $2,166.67 of interest in that month. Whatever's left of your fixed payment after interest goes to principal — which is why the principal share grows every single month as the balance falls.
Do extra payments lower my monthly payment?
No — they shorten the loan instead. Your required payment stays the same, but the loan ends earlier and you pay less total interest. If you want a lower payment, the tools for that are a refinance (see the refinance calculator) or a loan recast, where the lender re-amortizes your balance for a fee.
Is one lump sum better than the same amount spread monthly?
Dollar for dollar, earlier is better — a lump sum paid now starts reducing interest immediately, while the same total spread over years only helps gradually. Try it here: type a lump sum into a single month's extra column, then compare against the same total as a monthly amount in the scenario table above. The full mechanics are in our guide on how extra payments work.
When can I stop paying PMI?
On a conventional loan, you can request PMI removal once your balance falls to 80% of the home's original value, and lenders must cancel it automatically at 78%. Enter your home value in the form above and the ledger estimates the month you cross 20% equity through payments alone. Details and exceptions are in our PMI guide.
Should I pick a 15-year or 30-year term?
A 15-year loan carries a higher payment but usually a lower rate and dramatically less total interest; a 30-year loan buys flexibility. Run both terms through the calculator and compare the total interest lines — then read our 15 vs. 30 year breakdown for the trade-offs the raw numbers don't show.
Is anything I enter saved or sent anywhere?
No. Every calculation runs in your browser. Nothing you type is transmitted to a server or stored — refreshing the page resets it. See the privacy policy for how ads on this site work.
This tool is for general planning purposes only and isn't financial, legal, or lending advice. Speak with a licensed mortgage professional before making borrowing decisions.
More worksheets in the ledger
Refinance
Compare your current loan against a new rate and term, including closing costs and the breakeven month.
Form RVB‑02Rent vs. Buy
Total cost of renting against the net cost of owning over your time horizon, with equity counted properly.
Form AFD‑03Affordability
Work backward from income and debts to a realistic price range, using standard lender ratios.
Form GLS‑04Glossary
APR vs. note rate, points, escrow, PMI, recasting — mortgage vocabulary in plain language.
When to use this calculator
Verifying a lender's payment quote
A lender quotes you $2,528/month on a $400,000 loan at 6.5% over 30 years. Enter those numbers here. If the calculator returns the same figure, the arithmetic checks out. If it differs by more than a dollar or two, ask the lender what fees are included in their quoted payment that are not in yours — taxes, insurance, and mortgage insurance are the usual additions.
Understanding what a rate difference actually costs
The difference between 6.25% and 6.75% on a $400,000 loan sounds small. Run both and compare the total-interest lines. On a 30-year term the half-point difference in that example costs roughly $24,000 over the life of the loan — more than enough to justify shopping a second lender or paying a point to buy the rate down.
Finding the right extra-payment amount
You have $300 a month you could put toward the mortgage or invest elsewhere. Enter your loan details and add $300 to the extra-payment field. The calculator shows how many years that shaves off and how much interest it saves. That is your comparison point against whatever else the $300 might earn.
Planning for PMI removal
You bought with 10% down and want to know when you can drop PMI. Enter your current balance, rate, and remaining term, set the home value to your original appraised value, and read the PMI removal estimate. Then try adding a monthly extra and watch the date move forward.
Frequently asked questions
Why is my payment different from what my lender quoted?
The payment shown here is principal and interest only. Lenders typically quote a PITI payment — principal, interest, taxes, and insurance, often including mortgage insurance — all bundled into one figure. Subtract your estimated monthly taxes, insurance, and PMI from the lender's quote and the remainder should match this calculator closely. Small differences (under $5) are usually rounding.
Does this account for taxes and insurance?
No. The monthly payment shown is principal and interest only. Property taxes, homeowners insurance, flood insurance, and mortgage insurance premiums are not included. Your actual monthly payment sent to the servicer will be higher once those are escrowed.
Why does the amortization schedule show so much interest early on?
Because interest is calculated on the outstanding balance each month. With a large balance and 30 years ahead of you, the early payments carry a very high interest charge and a correspondingly small principal reduction. On a $400,000 loan at 6.5%, the very first payment allocates $2,167 to interest and only $361 to principal. That ratio gradually inverts as the balance falls, but it takes many years.
What is the crossover month and why does it matter?
The crossover month is when cumulative principal paid to date first exceeds cumulative interest paid. Before that point, if you add up every dollar you have ever sent to your servicer, more than half has gone to interest rather than equity. On a 30-year 6.5% loan the crossover is around year 18. It is a useful gut-check, not a decision rule, but it makes the front-loading of mortgage interest concrete.
How does the extra-payment calculation work?
The calculator builds two complete schedules: one with your extra payment, one without. The interest saved is the exact difference between the total interest on each schedule over its full length. The payoff date shown is from the accelerated schedule. Extra payments are applied to principal in the month they are made, after that month's interest has accrued. The full methodology is on the methodology page.
What does 'interest rate' mean here — note rate or APR?
The note rate. That is the rate used to compute your monthly payment and your amortization schedule. The APR (Annual Percentage Rate) is always higher because it folds in lender fees spread over the loan term. Use the note rate from your Loan Estimate, not the APR.
Sources
This calculator is an educational planning tool. Results are estimates based on the inputs and assumptions described on the methodology page. Nothing here is a loan offer, a rate quote, a pre-qualification, or financial advice. Verify every figure against your lender's official Loan Estimate or Closing Disclosure before making any decision.