Mortgage Calculator

How this mortgage calculator works

This calculator turns four numbers - home price, down payment, interest rate, and loan term - into the one figure that actually matters when you're buying a home: your true monthly payment. Unlike the calculators that show only principal and interest, it adds property tax, homeowners insurance, mortgage insurance, and HOA dues to give you the full picture, and it recomputes the instant you change anything. Every calculation runs in your browser. There are no ads, no email capture, and nothing you type is sent anywhere.

Below is exactly how the math works, so you can trust the number - and learn a little about how mortgages behave along the way.

The monthly payment formula

The principal-and-interest portion of a fixed-rate mortgage is a closed-form calculation. Given a loan amount, an interest rate, and a term, the monthly payment never changes - that's what "fixed-rate" means. The formula is:

M = P · r(1 + r)^n / ((1 + r)^n − 1)

where:

• M is the monthly principal-and-interest payment,
• P is the loan amount - the home price minus your down payment, not the home price,
• r is the monthly interest rate, equal to the annual rate divided by 12 (so a 6.5% annual rate is 0.065 / 12 ≈ 0.005417 per month),
• n is the total number of monthly payments - the term in years times 12 (a 30-year loan has 30 × 12 = 360 payments).

For example, a $300,000 loan at 6.5% over 30 years works out to a payment of about $1,896.20 per month. If the interest rate is 0%, the formula above would divide by zero, so the payment is simply the loan amount spread evenly across all payments: P / n.

What's in your payment: PITI

Lenders and real-estate pros talk about PITI - Principal, Interest, Taxes, and Insurance - because those four pieces make up a typical monthly housing payment. Showing only principal and interest understates what you'll really pay, sometimes by hundreds of dollars a month. This calculator always leads with full PITI:

Component	What it is	How it's estimated
Principal & interest	Repaying the loan plus the cost of borrowing	The formula above
Property tax	Local tax on the home's value, usually escrowed	Annual amount ÷ 12
Homeowners insurance	Coverage for the home, usually escrowed	Annual amount ÷ 12
PMI	Private mortgage insurance on low-down-payment loans	Loan amount × PMI rate ÷ 12
HOA dues	Homeowners-association fees, if any	Entered directly per month

Taxes and insurance are typically collected monthly into an escrow account and paid on your behalf when they come due, which is why they belong in your monthly number even though they aren't part of the loan itself.

How amortization works

Each month, your fixed payment is split between interest and principal - but the split changes over time. Interest is charged on the remaining balance, so early on, when you owe the most, most of your payment goes to interest. As the balance falls, more of each payment chips away at principal. This is called amortization, and it's why building equity feels slow at first and then accelerates.

The schedule is built one month at a time:

1. Interest for the month = remaining balance × monthly rate.
2. Principal for the month = your fixed payment − that interest.
3. New balance = old balance − principal (− any extra payment).

We carry full precision through every month and round only when displaying values, then reconcile the final payment so the loan lands exactly at a zero balance. You can view the schedule by year or expand it to every month, and export the whole thing to CSV with one click.

PMI and the 78% / 80% rules

If your down payment is under 20% of the home's value, a conventional loan generally requires private mortgage insurance (PMI) - an extra monthly charge that protects the lender, not you. The good news is that it doesn't last forever.

The federal Homeowners Protection Act defines two ways PMI comes off, and they work differently:

• Automatic termination at 78%. Your lender must cancel PMI once your loan balance reaches 78% of the home's original value. This date is fixed by your original payment schedule, so - perhaps surprisingly - extra payments do not move it. It's the guaranteed, no-paperwork outcome.
• Borrower-requested removal at 80%. Separately, you can ask your lender to drop PMI once you reach 80%, based on your actual balance. Because it uses your real balance, paying extra principal can get you there sooner. It assumes you request it, you're in good standing, and the home hasn't lost value.

By default this calculator shows the automatic 78% date and the exact month it lands. Switch the PMI option to "If I request removal at 80%" to see the earlier eligibility date instead - presented as an estimate of when you'd be eligible to ask, not a guaranteed drop. Put 20% down (or use the "Set 20%" shortcut) and PMI disappears entirely.

A couple of modeling notes: PMI here is a flat annual factor applied to your original loan amount (some servicers instead recompute it on the declining balance), and these rules are for conventional loans only. FHA, VA, and USDA loans handle mortgage insurance differently - FHA mortgage insurance, for instance, often does not cancel automatically - so treat the PMI here as a conventional-loan estimate.

The power of extra payments

Because interest is charged only on what you still owe, every extra dollar of principal is a dollar that stops accruing interest for the rest of the loan. That makes extra payments surprisingly powerful, especially early on.

Add a monthly extra or a one-time lump sum and the calculator shows two things: how many years and months you'd shave off the loan, and how much total interest you'd save versus the same loan with no extra payments. The chart even overlays a dashed "ghost" curve so you can see your balance crossing zero sooner. On a typical 30-year loan, an extra $100-$200 a month can cut years off the term and save tens of thousands in interest.

How much house can you afford? The 28/36 rule

A long-standing affordability guideline is the 28/36 rule: keep your monthly housing payment at or below 28% of your gross monthly income, and your total monthly debt payments at or below 36%.

Here's a worked example. Suppose your household earns $108,000 a year, or $9,000 a month before taxes.

• 28% of $9,000 is $2,520 - a target ceiling for your full PITI payment.
• 36% of $9,000 is $3,240 - a ceiling for housing plus car loans, student loans, credit-card minimums, and other debts.

So if you already pay $500 a month toward other debts, the 36% side leaves about $2,740 for housing, while the 28% side caps it at $2,520 - so $2,520 is your practical target. Plug a payment near that into the calculator and adjust price, down payment, and term until the monthly number fits. Remember it's a rule of thumb: lenders also weigh your credit score, cash reserves, and loan type, and some programs allow higher ratios.

Our methodology and assumptions

We built this tool correctness-first: the payment and amortization math is a pure, independently unit-tested engine, validated to the cent against known examples before any of the interface was built. A few assumptions worth knowing:

• Fixed-rate loans. The calculator models fixed-rate mortgages. Adjustable rates, interest-only periods, and balloon payments aren't included.
• Estimated defaults. Property tax, insurance, and PMI start from reasonable national estimates, clearly labeled and dated - and every one is editable. Real figures vary a lot by state, county, and lender, so adjust them to your situation. Auto-estimates you can't see or change are the fastest way to a wrong answer, which is why we surface and date all of them.
• Costs held flat. Property tax, homeowners insurance, and HOA dues are held constant for the life of the loan. In reality they tend to drift upward over time, so a payment decades out is likely understated.
• Note rate, not APR. The rate you enter is treated as the note (interest) rate. We don't fold in points, lender fees, or closing costs, so this is not an APR and shouldn't be compared directly to one.
• Conventional PMI only. As noted above, government-backed loans use different mortgage-insurance rules, and PMI is modeled as a flat factor on the original loan amount.
• An estimate, not an offer. This is an educational tool, not a loan quote or financial advice. Your actual rate and costs depend on your full financial picture and a lender's underwriting.

Want to share a scenario? Every number you change is saved to the page's web address, so you can copy the link and send your exact setup to a partner, agent, or loan officer - no account required.