Mortgage Calculator

How the mortgage calculator works

A mortgage is repaid through a process called amortization: a fixed payment, calculated once at closing, is applied every period for the life of the loan. In the earliest years, most of that fixed payment goes toward interest, because interest is charged on whatever balance remains. As the balance shrinks, a growing share of each payment goes toward principal, until the final payment clears the loan entirely. This calculator runs that same math instantly, recalculating every time you change an input, so you can compare scenarios without waiting on a lender or spreadsheet.

Behind the big monthly number, three separate calculations are happening. First, the calculator solves for a fixed principal-and-interest payment using your loan amount, interest rate, and term. Second, it layers on the recurring costs of homeownership that lenders typically collect through an escrow account: property tax, homeowners insurance, private mortgage insurance if applicable, and HOA dues if the property has one. Third, if you've entered an extra payment or chosen biweekly or weekly frequency, it simulates the loan month by month (or period by period) to show exactly how much faster the balance falls and how much interest that avoids.

The amortization formula

The fixed principal-and-interest payment is calculated with the standard amortization formula used by virtually every mortgage lender in the United States:

Each period, interest due is calculated as the current balance multiplied by the periodic interest rate. Whatever is left of the fixed payment after interest is subtracted goes toward principal, permanently reducing the balance that next period's interest is calculated on. That compounding relationship is why extra payments made early in a loan are worth more than the same extra payment made later: a dollar of principal paid off in year two keeps saving interest for the next 28 years, while a dollar paid off in year twenty-nine only saves interest for one year.

A worked example

Take a $450,000 home with a 20% down payment of $90,000, leaving a $360,000 loan at a 6.75% fixed rate over 30 years. Converting the annual rate to a monthly rate gives 0.005625, and the term is 360 monthly payments. Plugging those numbers into the formula above produces a fixed principal-and-interest payment of roughly $2,335 per month. In the very first month, interest on the full $360,000 balance is about $2,025, leaving only around $310 to reduce principal. By year fifteen, the balance has fallen enough that the split is roughly even, and by the final years of the loan, almost the entire payment goes toward principal. Add estimated property tax, homeowners insurance, and PMI (since the down payment is exactly 20%, PMI may or may not apply depending on the lender and loan type), and the full monthly housing payment lands close to $2,900 to $3,000 — which is the figure this calculator's results panel shows as "Payment."

A second example: choosing a 15-year term instead

Now take that same $360,000 loan and run it over 15 years instead of 30. Lenders typically price shorter terms lower, so assume a rate of 6.0% rather than 6.75%. The monthly rate becomes 0.005, the term becomes 180 payments, and the fixed principal-and-interest payment rises to roughly $3,037 — about $700 more per month than the 30-year option. In exchange, total interest paid over the life of the loan falls from well over $400,000 on the 30-year schedule to around $186,000 on the 15-year schedule, a swing of more than $200,000. Equity also builds far faster: by year seven, more than half the loan is typically paid off on a 15-year term, compared to roughly a quarter on a 30-year term at the same point. Whether the higher payment is worth it depends entirely on your monthly budget and how much you value building equity quickly versus keeping payments flexible.

How much house can you actually afford?

Most lenders lean on two ratios to size a maximum mortgage payment: the front-end ratio, which caps your total housing payment (PITI) at roughly 28% of gross monthly income, and the back-end ratio, which caps all debt payments combined, including the mortgage, at roughly 36% to 43% of gross monthly income depending on the loan program. A household earning $9,000 a month before taxes, for example, would generally be guided toward a housing payment no higher than about $2,520 under the front-end rule, though approval limits can run higher with strong credit and low existing debt.

Those ratios set a ceiling, not necessarily a comfortable target. Many financial planners suggest budgeting closer to 25% of take-home (after-tax) pay for housing rather than gross income, which leaves more room for savings, maintenance, and the inevitable surprises of homeownership. Use this calculator to work backward: start from a monthly payment you're confident you can sustain, then adjust the home price, down payment, and term until the "Payment" figure in the results panel lines up with that number.

Two overlooked factors change the true affordability picture. First, closing costs typically run 2% to 5% of the loan amount and are due in cash at closing, separate from your down payment — budget for both. Second, homeownership carries ongoing costs this calculator doesn't model directly, including maintenance (often estimated at 1% of home value per year), utilities that tend to run higher than renting an equivalent apartment, and the opportunity cost of the down payment itself.

Refinancing: when it makes sense

Refinancing replaces your existing mortgage with a new one, usually to secure a lower rate, change the term, or convert equity to cash. As a rule of thumb, refinancing tends to make financial sense when the new rate is at least 0.5 to 1 percentage point below your current rate and you plan to stay in the home longer than the break-even period — the time it takes for monthly savings to exceed the closing costs of the new loan. You can approximate that break-even point by running your current loan's remaining balance and term through this calculator at a lower rate, comparing the new payment to your current one, and dividing estimated refinance closing costs by the monthly savings.

Beyond chasing a lower rate, refinancing is also commonly used to drop mortgage insurance once enough equity has built up, to convert an adjustable-rate loan into a fixed rate before an adjustment period begins, or to shorten a term from 30 years to 15 once income has grown enough to absorb a higher payment. Each of these is worth modeling here first — plug in the new rate, remaining balance, and remaining or reset term to see the real dollar impact before paying any refinance application fees.

Step-by-step: using this calculator

1. Enter the home price and down payment. Type either a dollar down payment or a percentage — the calculator keeps both fields in sync automatically, and the loan amount updates instantly below.
2. Set your interest rate and term. Use the rate quoted by your lender or a current market average for planning purposes, and choose 30, 20, 15, or 10 years, or enter a custom term.
3. Add taxes, insurance, PMI, and HOA. Toggle each item on or off to see how it affects your total payment; uncheck any that don't apply to your situation.
4. Choose a payment frequency. Switch to biweekly or weekly to see the payoff-acceleration effect of paying more often without changing your interest rate.
5. Add an extra payment (optional). Enter any additional amount you plan to put toward principal each month to see your new payoff date and total interest savings.
6. Review your results. The results panel, balance chart, payment composition chart, and yearly schedule all update together, and each can be copied, printed, shared, or exported.

Understanding your results panel

The headline number is your total recurring payment at the frequency you selected. Below it, the donut chart and legend break that payment into its components: principal and interest (P&I), property tax, home insurance, PMI, and HOA, so you can see at a glance which piece of your budget is largest. The summary grid adds three big-picture figures — total interest paid over the life of the loan, total cost of the loan (principal plus interest), and your projected payoff date — along with your current loan-to-value ratio, which matters because it determines whether PMI applies and when it's scheduled to fall away.

Benefits of using a mortgage calculator before you shop

Tips for lowering your mortgage payment

Common mortgage mistakes to avoid

Extra payments and early payoff strategies

Because interest is calculated on the remaining balance, any extra amount applied directly to principal stops accruing interest immediately and for every remaining period of the loan. That's why even a modest extra payment, sustained over years, can remove several years from a 30-year term and save a substantial amount in interest — often tens of thousands of dollars on a typical loan. The calculator above simulates this precisely: it re-runs the amortization period by period with your extra payment subtracted from the balance, then reports the new payoff date and the interest avoided compared to the standard schedule.

Biweekly payment plans work through a similar mechanism from a different angle. Splitting your monthly payment in half and paying every two weeks results in 26 half-payments a year — the equivalent of 13 full monthly payments instead of 12. That extra payment, applied once a year, produces a payoff acceleration similar to a modest extra monthly payment, without requiring you to find additional money each month, since it simply reshuffles the same annual amount into more frequent installments.

Fixed-rate vs. adjustable-rate mortgages

This calculator models a fixed-rate loan, where the interest rate and the principal-and-interest payment never change for the life of the loan — the predictability most buyers want for long-term budgeting. An adjustable-rate mortgage (ARM) typically offers a lower introductory rate for a set period, often five, seven, or ten years, after which the rate adjusts periodically based on a market index. ARMs can make sense for buyers who expect to sell or refinance before the adjustment period begins, but they carry the risk that payments could rise if rates move upward before that happens. If you're comparing a fixed-rate and an ARM offer, run both through this calculator at their respective rates to compare the payment difference during the introductory period.

Reading your amortization schedule

The schedule tab groups every payment by calendar year, showing how much of that year's payments went to principal, how much went to interest, and what your balance was at year's end. Click any year to expand it into individual payments, which is the clearest way to see the interest-to-principal split shift over time — early rows show interest dominating the payment, later rows show principal dominating it. The "Escrow & fees" column reflects property tax, insurance, PMI while it applies, and HOA dues, none of which reduce your loan balance; only the principal column does that. If you're evaluating whether to sell or refinance in a given year, the ending-balance column for that year is the fastest way to estimate your remaining loan balance and, combined with an estimated home value, your available equity.

Is mortgage interest tax-deductible?

In the United States, homeowners who itemize deductions can generally deduct interest paid on mortgage debt up to current federal limits, which depend on when the loan originated and the total balance. Because the deduction applies to interest, not principal, and interest makes up the majority of early payments, the deduction is typically largest in the first years of the loan and shrinks as the interest portion of each payment declines. Whether itemizing beats the standard deduction depends on your total deductions across categories, so this is worth reviewing with a tax professional rather than assuming it automatically reduces your effective rate — this calculator does not model tax effects.

Mortgage terminology explained

Principal

The portion of your loan balance still owed, separate from interest. Every payment reduces principal by a growing amount over time.

Interest

The cost of borrowing, calculated as a percentage of your remaining balance and charged each period until the loan is paid off.

PITI

Shorthand for principal, interest, taxes, and insurance — the four components most lenders bundle into a single monthly mortgage payment.

PMI

Private mortgage insurance, typically required on conventional loans when the down payment is below 20%, protecting the lender if the borrower defaults.

Escrow account

A holding account managed by your loan servicer that collects a portion of your payment each month and pays property tax and insurance bills on your behalf.

Amortization

The schedule by which a loan is paid off through regular payments, each split between interest and principal according to the remaining balance.

Loan-to-value (LTV)

Your loan balance divided by the home's value, expressed as a percentage — a key figure lenders use to price risk and determine PMI requirements.

APR

Annual percentage rate, a broader measure than the interest rate alone that also reflects certain lender fees, useful for comparing offers.

Discount points

Optional upfront fees paid at closing in exchange for a lower interest rate over the life of the loan.

HOA dues

Recurring fees paid to a homeowners association for shared amenities and maintenance, common in condos and planned communities.

Escrow shortage

A gap that occurs when actual tax or insurance bills exceed what was collected, usually resulting in a temporary payment increase to catch up.

Payoff date

The projected date your final payment clears the loan balance to zero, based on your current schedule and any extra payments.

Equity

The difference between your home's current market value and your remaining loan balance — it grows both as you pay down principal and as the home appreciates.

Debt-to-income ratio (DTI)

Your total monthly debt payments, including the proposed mortgage, divided by your gross monthly income; lenders use it to size the maximum loan you qualify for.

Rate lock

A lender's commitment to hold a specific interest rate for a set period while your loan is processed, protecting you from rate increases before closing.

Closing costs

One-time fees due at signing, typically 2% to 5% of the loan amount, covering items like appraisal, title insurance, origination fees, and recording fees.

Methodology and accuracy

This calculator uses the standard fixed-rate amortization formula applied by mortgage lenders across the United States, simulating your loan payment by payment so that extra payments, PMI removal, and biweekly or weekly schedules are reflected in the actual balance and interest, rather than approximated. PMI is modeled using the common industry convention of automatic removal once the balance is scheduled to reach 78% of the original home value, matching the federal Homeowners Protection Act baseline; individual lenders and loan types (such as FHA loans, which follow different PMI-equivalent rules) may vary. Property tax, homeowners insurance, and HOA figures are entered by you and are only as accurate as your inputs — for a firm number, use your county assessor's site for tax estimates and a current insurance quote rather than a placeholder. All figures update live in your browser; no data you enter is transmitted or stored.