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Mortgage Calculator

Estimate monthly mortgage payments, total interest and total cost. Includes full amortization schedule.

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How to Use the Mortgage Calculator

  1. Enter the home price - the agreed purchase price from the sale contract, not a rough estimate.
  2. Enter your down payment - the cash you will put up at closing. Twenty percent is the classic threshold that eliminates PMI on conventional loans; 3-5% is common on FHA and first-time-buyer programs.
  3. Enter the annual interest rate - the rate quoted by your lender on the Loan Estimate form. Use the note rate, not the APR, for an amortization-accurate calculation.
  4. Choose the loan term - select 10, 15, 20, 25, or 30 years. The 30-year fixed is the most common US mortgage; 15-year saves roughly half the total interest for a higher monthly.
  5. Review the output and schedule - the calculator displays monthly principal-and-interest, total interest over the life of the loan, total cost, and a breakdown bar. Clicking "Show Amortization Table" reveals the month-by-month split between principal and interest.

The Math and What This Tool Actually Models

This is a fixed-rate amortization calculator. It solves the standard Time Value of Money equation M = P × r(1+r)n / ((1+r)n - 1) for the monthly payment M, using monthly periodic rate r and total payments n. The amortization schedule then iterates forward: each month's interest is the outstanding balance times r, the remaining portion of M reduces principal, and the new balance carries into the next row. This is precisely the method defined in the Consumer Financial Protection Bureau's mortgage disclosure guidance and produces numbers that match your lender's billing system to within a cent per payment.

The calculation runs as a Preact island; inputs use parseFloat, the iteration runs a single pass of n steps, and formatting uses Intl.NumberFormat with USD locale. The computation is client-side: no balance, rate, or personal detail is sent to any server, because there is no fetch, XHR, or beacon for those values. You can confirm this by opening the Network tab in Chrome or Firefox devtools and watching traffic freeze after the initial page load while you edit inputs.

When This Calculator Earns Its Keep

  • Pre-shopping for a home - plugging in the target monthly payment you can sustain and working backwards to a realistic home price.
  • Comparing a "no-points" 7.0% quote against a "1-point buydown" 6.625% quote to see the break-even month.
  • Sanity-checking a mortgage broker's verbal estimate before receiving the formal Loan Estimate - the TRID rule gives lenders three days to issue it.
  • Running a refinance analysis: current rate and balance versus a new-loan quote, accounting for closing costs rolled in.
  • Deciding whether to recast a mortgage (pay down a lump sum and re-amortize) after receiving a bonus or inheritance.
  • Modeling how a 2% down-payment increase changes your PMI exposure and monthly cost.

Edge Cases You Want to Be Aware Of

This calculator does not include PITI components beyond principal and interest. Your actual monthly housing cost bundles property tax (roughly 1.1% of home value annually in the US, but ranging from 0.3% in Hawaii to 2.4% in New Jersey), homeowners insurance ($1,400-2,000 per year national average), and private mortgage insurance if your LTV exceeds 80%. PMI itself is usually 0.5-1.5% of the loan annually and is required on conventional loans until you request cancellation at 80% LTV or automatic termination at 78% per the Homeowners Protection Act. FHA loans carry MIP for the life of the loan in most post-2013 cases. Adjustable-rate mortgages (ARMs) do not stay fixed - a 5/1 ARM locks the rate only for the first five years and then resets annually against an index plus margin, so this calculator gives a valid figure only for the initial period. Interest-only and balloon mortgages also violate the fully-amortizing assumption.

The Mortgage Landscape in Two Paragraphs

US residential mortgages are dominated by conventional loans (conforming to Fannie Mae and Freddie Mac limits, $766,550 for most counties in 2024, higher in designated high-cost areas), FHA loans (3.5% minimum down, backed by HUD, for moderate-income buyers), VA loans (for eligible veterans, often 0% down, no PMI), and USDA loans (rural, 0% down, income-capped). Jumbo loans exceed the conforming limit and carry their own underwriting. All of these can be fixed-rate (30, 20, 15, or 10-year) or adjustable. The amortization formula above is the same across all product types - only the rate, term, and insurance add-ons vary.

The mortgage process is governed by TILA, RESPA, and the TRID rule, which together require a Loan Estimate within three business days of application and a Closing Disclosure three business days before closing - both forms use standardized layouts so you can compare offers line by line. APR on the Loan Estimate includes mortgage insurance, origination, discount points, and certain third-party fees, and is the right figure for comparing two offers; the note rate used in this calculator is correct for the amortization math but hides fee differences.

How This Tool Stacks Up Against Bankrate, Zillow, and Your Lender's Site

Bankrate, NerdWallet, and Zillow all ship mortgage calculators with more fields (PITI escrow, PMI, HOA) that produce a more realistic total-monthly number - useful when you are nearing a decision. Their downside is lead capture: they often route your inputs to lender partners. Your lender's own site gives the most accurate figure because it ties to their actual product pricing, but only works for quotes from that lender. Excel's PMT(rate/12, nper, -pv) returns an identical monthly-payment figure. This calculator's niche is speed for the principal-and-interest piece: three or four inputs, instant amortization table, no tracking scripts collecting your targeted home price. The output is for education and planning only; a licensed loan officer, a real-estate attorney, and ideally a fee-only financial planner should review any mortgage commitment before signing.

Frequently Asked Questions

Why does the amortization schedule front-load interest so heavily?

Because interest each month is charged on the outstanding balance, and the balance is largest at the beginning. On a $300,000 30-year loan at 6.5%, the first monthly payment of about $1,896 applies roughly $1,625 to interest and only $271 to principal. The principal portion grows every month as the balance falls; around year 22 the split crosses 50/50. This is standard amortization behavior, not a lender tactic.

What is PMI and when do I stop paying it?

Private Mortgage Insurance protects the lender if you default. It is required on conventional loans when your loan-to-value exceeds 80%. Under the federal Homeowners Protection Act, PMI must automatically terminate when scheduled LTV reaches 78% based on the original amortization schedule, and you can request cancellation at 80% LTV based on either scheduled or appraised value. FHA loans have their own Mortgage Insurance Premium, which for most loans originated after 2013 runs for the life of the loan regardless of equity.

Should I pay points to lower my rate?

Each discount point costs 1% of the loan and typically lowers the rate by about 0.25%. The break-even is total point cost divided by monthly savings - commonly 5-7 years. If you expect to keep the loan longer than the break-even and are not planning to refinance, points can make sense. If you might sell or refinance within 5 years, paying for them rarely pays off. This calculator can model the post-points rate directly; compare total-cost outputs at each rate to see the difference.

How do I use this for a refinance decision?

Run the calculator twice: once with your current rate and remaining balance over the remaining years, once with the proposed new rate and term and balance that includes rolled-in closing costs. Compare monthly payment, total interest, and time to payoff. A common decision rule is that refinancing is worthwhile if the new rate is at least 0.75-1.00% below the current rate and you will stay in the home at least 2-3 years to recoup closing costs.

Is my mortgage information kept private?

Yes. This calculator is a static page with a Preact component that holds inputs in memory only. No balance, rate, or home-price figure is sent to a server, and there is no analytics payload carrying those values. Closing the browser tab discards every input. You can verify by checking the Network tab in your browser devtools while editing fields.

What is the difference between interest rate and APR?

The interest rate is the raw cost of borrowing principal and drives your amortization. APR (Annual Percentage Rate) is defined under Regulation Z and adds mandatory costs - origination, mortgage insurance premiums on FHA, discount points, certain third-party fees - spread across the life of the loan. APR is always at least as high as the note rate. Use APR for comparing two lender offers on identical products; use note rate for amortization math.

Why is my monthly payment different from what the bank quoted?

Most likely because the bank quoted PITI (principal, interest, taxes, insurance) and this calculator shows only principal and interest. Property tax and homeowners insurance typically add $300-600 per month on a median-priced home. If you are putting down less than 20%, PMI or MIP adds another $100-300. Also confirm the bank is using the note rate versus APR and that the loan term matches.

Can a 15-year mortgage save me money if I can afford the higher payment?

Usually yes, but it depends on what you would do with the payment difference. On a $300,000 loan at 6.5% (30-year) versus 5.75% (15-year), the 30-year pays about $383,000 in interest versus $148,000 for the 15-year, but the 15-year monthly is about $700 higher. If you would reliably invest that $700 per month in equities, a 30-year plus investing can outperform. If the $700 would otherwise be spent, the 15-year is the disciplined choice.

What happens if I pay extra principal each month?

The extra reduces the loan balance immediately, which cuts the interest charged in every subsequent month. On a $250,000 30-year loan at 6.5%, adding $200/month in extra principal pays the loan off about 7 years early and saves roughly $92,000 in interest. Make sure your servicer applies extra payments to principal (not to future interest) - most now do this automatically, but confirm with the first extra payment.

Should I trust this calculator instead of talking to a loan officer?

For quick amortization math, yes - the numbers are mathematically exact. For an actual borrowing decision, no. A licensed loan officer or mortgage broker evaluates your credit profile, debt-to-income ratio, and documented income to produce a real offer, and a Loan Estimate gives you the full cost. Combine this calculator for speed with a human for accuracy, and ideally a fee-only financial planner for whether the mortgage fits your broader financial plan.

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