Mortgage Calculator

What this calculator does

This is a monthly mortgage payment estimator. You type in six numbers describing the home you're buying and the loan terms, and it shows you the monthly payment broken into its parts: principal and interest, property tax, homeowner's insurance, and PMI (private mortgage insurance) when it applies. The total at the bottom is the sum of all four.

It's the kind of "PITI" calculator real estate agents and loan officers use when you ask "what would this house cost me a month?" The advantage of doing it yourself is that you can run twenty scenarios in two minutes without anyone trying to sell you anything. Every recalculation happens in your browser as you type. There is no Calculate button, no signup, no email capture, and no number you enter is sent anywhere.

Who actually needs this

• House hunters comparing listings. The Zillow estimate on a listing is fine for a first glance, but it usually assumes a 20% down payment and a default interest rate that may not match what you can get. Plugging your own numbers in is more honest.
• People deciding how much to put down. The PMI line shows up the moment you drop below 20% down, and disappears the moment you reach it. Sliding the down payment up and down is the fastest way to see what that 20% threshold actually saves you per month.
• Anyone shopping rates. Quarter-point rate moves don't feel like much until you see them as monthly dollars. A 6.5% vs 6.75% rate on a $280,000 loan is roughly $46 a month, or about $16,600 over 30 years.
• Refinance candidates. Compare your current payment to what a new rate and remaining term would produce. If you're staying long enough to break even on closing costs, refinancing is worth doing.
• Renters trying to figure out what they can afford. Start with a monthly number you can stomach and work backwards by adjusting the home price until the total monthly comes out right.

The six inputs, what they mean, and how to type them

All six fields are plain number inputs. There are no sliders, no currency formatting, no percent signs to enter. You type raw numbers.

• Home Price — the full purchase price in whole dollars (e.g. 350000, not $350,000 and not 350k). This is the price you and the seller agreed on, not the appraisal and not the assessed value.
• Down Payment — what you're paying up front in dollars (e.g. 70000). The loan amount the calculator uses is simply Home Price − Down Payment. If you leave this blank it's treated as zero, which means you're financing 100% of the price.
• Interest Rate — the annual interest rate as a plain percent (e.g. 6.5, not 0.065 and not 6.5%). Use the rate, not the APR. APR includes some fees and is used to compare loan offers, not to compute the payment.
• Loan Term — the length of the loan in years (e.g. 30, 20, or 15). The math converts this to months internally.
• Annual Property Tax — your yearly property tax bill in dollars (e.g. 4200). Not monthly. If you don't know it yet, a rough rule is to multiply the home price by your county's effective rate (often somewhere between 0.5% and 2.5% depending on where you live). You can usually find the exact figure on the listing or the county assessor's website.
• Annual Insurance — your yearly homeowner's insurance premium in dollars (e.g. 1200). For a quick estimate before you have a real quote, a common ballpark is 0.3% to 0.5% of the home price per year.

Three of the six fields are required: Home Price, Interest Rate, and Loan Term. If any one of those is blank or zero, the results panel stays hidden. The other three (down payment, property tax, insurance) are optional and default to zero if you skip them.

How the math actually works

Three different formulas are stacked together. None of them are exotic. If you've ever seen a mortgage explained, you've seen these.

Principal and interest

This is the standard fixed-rate amortization formula:

M = P × [ i(1 + i)^n ] / [ (1 + i)^n − 1 ]

where P is the loan principal (home price minus down payment), i is the monthly interest rate (the annual rate divided by 100, then divided by 12), and n is the total number of payments (loan term in years times 12).

This is the payment that, paid every month for the full term, ends with the loan exactly paid off. It doesn't change month to month. What does change is how that fixed payment is split between interest and principal: in the early years it's mostly interest, and as the balance falls, more of each payment chips away at the principal.

Property tax and insurance

Both of these are annual figures you enter directly. The calculator divides each by 12 to get the monthly portion and adds them on top of the principal and interest. They don't change the amortization math; they're flat add-ons. This matches how lenders escrow them: each month you pay 1/12 of the annual amount into an escrow account, and the lender pays the bills when they come due.

PMI

Private mortgage insurance is the cost of being allowed to put down less than 20%. The lender requires it because a low-down-payment loan is riskier for them.

The rule here is strict: if your down payment is less than 20% of the home price, PMI gets added. If it's exactly 20% or more, PMI is zero. The estimate is a flat 0.5% of the loan amount per year, charged monthly:

PMI = (Loan Amount × 0.005) ÷ 12

The total

The bottom line is simply principal and interest + monthly tax + monthly insurance + monthly PMI.

A worked example with the default placeholders

If you type the placeholder values exactly — 350000 home price, 70000 down, 6.5 rate, 30 years, 4200 tax, 1200 insurance — here is what comes back:

• Loan principal: $280,000 (350,000 − 70,000)
• Monthly rate: 0.5417% (6.5 ÷ 100 ÷ 12)
• Number of payments: 360 (30 × 12)
• Principal and Interest: $1,769.79
• Monthly Property Tax: $350.00 (4,200 ÷ 12)
• Monthly Insurance: $100.00 (1,200 ÷ 12)
• Monthly PMI: $0.00 (down payment is exactly 20%, so no PMI)
• Total Monthly Payment: $2,219.79

Now drop the down payment to $50,000 and rerun. The loan principal jumps to $300,000, principal and interest rises to about $1,896.20, and PMI kicks in at 300,000 × 0.005 ÷ 12 = $125.00 per month. The total climbs to roughly $2,471.20. That extra $20,000 down was buying you about $251 in monthly relief, or about $3,000 a year, until you reach 20% equity and PMI falls off (which on this loan would take several years on its own).

Sensible defaults if you're just trying numbers

If you don't have real figures yet and you're just sketching what might be possible, these starting points are close enough to be useful:

• Interest rate. Whatever current 30-year fixed rates are running for someone with your credit. Don't use a number you heard your parents quote from 2015.
• Loan term. 30 years for the standard case. Try 15 years on the same loan and look at the principal-and-interest difference; you'll pay roughly 40% more per month but save a huge amount in lifetime interest.
• Down payment. 20% if you want to avoid PMI, or whatever you actually have saved if you don't. Try both and look at the PMI line.
• Property tax. 1% of the home price per year is a rough national-ish average, but it varies enormously by state and county. Texas and New Jersey are high; Hawaii and Alabama are low. Replace this with the real number from the listing before making a real decision.
• Insurance. 0.35% of the home price per year is a reasonable placeholder until you get a real quote.

What the result does and doesn't include

What it includes: principal, interest, property tax, homeowner's insurance, and PMI when down payment is under 20%. That's the four components of "PITI" plus PMI — the bundle most lenders quote when you ask for a monthly payment.

What it doesn't include:

• HOA dues or condo fees. If the property has them, add them on top yourself.
• Closing costs and points. These are one-time costs at signing, not monthly. They typically run 2% to 5% of the loan amount. Discount points lower your rate but cost cash up front; a points calculator is the right tool for that trade-off.
• Mortgage insurance for FHA and VA loans. FHA has its own MIP (with both upfront and ongoing components) that doesn't follow the 0.5% rule used here. VA loans don't have monthly PMI but have a one-time funding fee. The PMI line in this tool is the simple conventional-loan version.
• The standard deduction or any tax benefit from mortgage interest. This is a gross payment, not an after-tax cost.
• Utilities, maintenance, or repairs. Budget separately for these. A common rough estimate is 1% of the home's value per year for maintenance.
• The fact that real PMI eventually falls off. By law, conventional PMI cancels automatically when you reach 22% equity based on the original purchase price, and you can request cancellation at 20%. This calculator shows a single steady monthly snapshot — it doesn't model PMI dropping off in year seven.

Common pitfalls and how to avoid them

• Typing the rate as a decimal. Enter 6.5 for 6.5%, not 0.065. If your payment comes back as something tiny like $4 a month, this is what happened.
• Treating monthly tax and insurance figures as if they were the annual ones. The fields say Annual for a reason. If you type your monthly escrow figure here, your total will be 12 times too low on those lines.
• Forgetting the down payment is in dollars, not percent. A 20% down on a $350,000 home is 70000, not 20.
• Reading the result as the lender's official quote. Real lenders round, sometimes use a slightly different day-count convention, and add their own fees. The number here will be within a few dollars of theirs but rarely matches to the cent.
• Forgetting HOA dues. If the house is in an HOA, that monthly fee is real money that the calculator doesn't know about. Some HOAs are $50; some condo HOAs are $800. Add it separately.
• Comparing rates without comparing terms. A 6.5% 30-year and a 6.0% 15-year aren't the same product. The monthly payment is dominated by the term, not the rate.

What to do if the result looks wrong

If no result appears at all, one of the three required fields (home price, interest rate, or loan term) is blank or zero. Check those first.

If the principal-and-interest figure looks much too high or too low, the most common culprit is the interest rate field. Re-read it: 6.5, not 0.065, and not 65. Then check whether the loan term you typed is in years or months — it expects years, so a 30-year loan is 30, not 360.

If PMI shows up when you weren't expecting it, check the down payment dollar amount against the home price. The threshold is strictly less than 20%; 19.99% down still produces PMI. If PMI is missing when you expected it, your down payment is at or above 20% of the home price.

If the total monthly is wildly higher than a lender's quote, the most likely cause is property tax or insurance entered as a monthly figure instead of an annual one. Multiply both by 12 in your head; if either lands at "this would be a huge yearly bill," you typed an annual amount as monthly.

Scenarios worth running

• The 20% threshold. Type the same home price and rate, and slide the down payment from just under 20% to just at 20%. Watch PMI snap to zero. That number is what putting down 20% is actually saving you per month.
• 15 vs 30 years. Same loan, same rate, flip the term. Higher monthly payment but dramatically less total interest over the life of the loan. If you want the lifetime numbers, multiply principal-and-interest by 12 and by the term — the difference between the two totals is what the longer term costs you in interest.
• Rate shopping. Hold everything else constant and step the rate by 0.25% increments. This shows you in concrete dollars whether paying for points or shopping a few more lenders is worth it.
• Stretching the price. If you have a maximum monthly payment in mind, adjust the home price upward until the total monthly hits your number. That tells you what listing prices to actually browse.
• Comparing two cities. Use the same home price and rate but different property tax figures. Property tax differences between states or counties can dwarf the rate differences people obsess over.

When this calculator isn't the right tool

• Adjustable-rate mortgages (ARMs). This assumes a single fixed rate for the entire term. An ARM will have a different payment after the introductory period ends.
• Interest-only loans, balloon loans, or anything with a non-standard structure. The amortization formula here assumes a level monthly payment that fully pays the loan off at the end.
• FHA, VA, or USDA loans where mortgage insurance is a real piece of the cost. The 0.5% PMI estimate is a conventional-loan placeholder and is the wrong model for FHA's MIP, VA's funding fee, or USDA's guarantee fee.
• Affordability checks that need debt-to-income ratios. Lenders qualify you based on your total monthly debt against your gross income (the front-end and back-end DTI ratios). A monthly payment is one input to that calculation, not the calculation itself.
• Build or renovation loans. Construction loans draw down over time and convert to a permanent mortgage at the end. Different shape entirely.
• Locked-in lender quotes. If you have a Loan Estimate in hand, trust that document over any web calculator. It has your real rate, real fees, and a guaranteed monthly payment to the cent.

Adjacent concepts worth knowing

PITI. Principal, Interest, Taxes, Insurance. The bundle of four numbers most lenders quote and most escrow accounts collect. This calculator is a PITI calculator that also adds PMI on top when it applies.

Amortization. The process of paying down a loan with fixed monthly payments where each payment is split between interest on the remaining balance and principal reduction. The split shifts over time even though the payment stays flat — early on it's mostly interest, late on it's mostly principal.

Loan-to-value ratio (LTV). Loan amount divided by home value. PMI keys off this: when LTV exceeds 80% (i.e. down payment is less than 20%), PMI applies.

Escrow. The account your lender uses to collect 1/12 of your annual tax and insurance bills each month and pay them when they're due. The monthly tax and insurance figures in this calculator match the escrow portion of your bill.

APR vs interest rate. The interest rate is what computes your payment. The APR rolls certain fees into a comparable rate and is intended to help you compare loan offers. Use the rate here, not the APR; using APR will overstate your payment.

Points. One discount point is 1% of the loan amount paid up front in exchange for a lower rate (commonly about 0.25% off, though it varies). To see whether paying points pays off, run the calculator with and without the lower rate and divide the monthly savings into the up-front cost. That's your breakeven month.