How much house can I afford?

The calculator inverts the arithmetic a lender runs. It starts from your gross monthly income, takes the share a debt-to-income limit allows for all debt payments, subtracts the debts you already carry, and treats what remains as the most you can spend on housing each month. Then it finds the highest price whose full monthly cost equals that budget. There is one exception, covered further down: right at the 20% line the down payment caps the price before the budget runs out, and the answer leaves part of the budget unspent.

The full monthly cost has five parts. Principal and interest on the loan, from the standard amortization formula at your rate and term. Property tax, as a percentage of the price spread across twelve months. Homeowners insurance, as an annual premium divided by twelve. Private mortgage insurance, as a percentage of the loan, added only when the down payment is under 20% of the price. And HOA dues, if you enter them.

Because tax scales with the price and interest scales with the loan, the price is solved in closed form rather than guessed. The engine solves once without mortgage insurance and once with it, checks which solution is consistent with its own loan-to-value, and takes the 20% boundary itself when the two disagree. Every figure on this page and in the JSON twin comes from that one function, so the two never drift.

Cash to close is reported beside the monthly payment but is not part of the solve. It is the down payment plus closing costs at a percent of the price, the lender, title, appraisal, and prepaid items that are paid once at the table. Closing costs do not change the price the ratio allows; they change how much of your savings the price consumes, which is why a down payment alone understates what you need in the bank.

The defaults are published statistics, not guesses: the weekly Freddie Mac survey rate, the effective property tax rate from Census data, the countrywide average homeowners premium from state regulators, the debt-to-income ceilings in Fannie Mae's Selling Guide, and Freddie Mac's published ranges for mortgage insurance and closing costs. Each one names its source and as-of date beside the field, under the assumptions line, and each can be replaced by your own number.

Debt-to-income is the ratio of all monthly debt payments, including the proposed housing payment, to gross monthly income. It is the single rule that does most of the work in an affordability calculation, which is why the calculator puts the choice under the number and shows the price at each ceiling a lender might use.

Fannie Mae Selling Guide B3-6-02, Debt-to-Income Ratios sets a maximum total ratio of 36% for manually underwritten loans, raised to 45% when the borrower meets its credit score and reserve requirements, and allows up to 50% for loans run through Desktop Underwriter. Those three numbers are the 36%, 45%, and 50% options under the number. The 28/36 option keeps the 36% total and adds the classic 28% housing limit as a second ceiling, which is what the most conservative rule of thumb amounts to.

The calculator defaults to 36% because it is the floor every program accepts. Raising it raises the price, and the page says so in the warnings: at 45% or 50% the number depends on approvals that not every borrower gets, and any ratio above 50% sits outside the conforming programs entirely. A higher ratio also means a larger share of every paycheck is spoken for before groceries, which is the practical reason the rule of thumb stays conservative.

The optional front-end ratio caps the housing payment alone as a share of income. Some lenders and most rules of thumb use 28%. The calculator leaves it off because Fannie Mae's guide does not require one, but the 28/36 option turns it on, and when it is the tighter of the two limits the result says that it set the price.

At the published defaults, a household earning $100,000 a year with no other monthly debt and $40,000 saved for the down payment can afford a home priced around $410,391. The total monthly payment is $3,000: $2,378 of principal and interest on a $370,391 loan, $304 of property tax, $133 of insurance, and $185 of mortgage insurance because the down payment is 9.7% of the price. Cash to close is $54,364: the $40,000 down payment plus $14,364 of closing costs at 3.5% of the price.

The same salary with $500 a month of car or student loan payments affords $345,114, because every dollar of other debt comes straight out of the housing budget. And the same salary with $92,000 down, the smallest round figure that clears the 20% line and drops mortgage insurance, affords $460,000. The down payment does double duty: it lowers the loan and removes a monthly charge.

Here is the same calculation across common salaries, at the default rate of 6.65% over 30 years with $40,000 down, with and without $500 a month of other debt. Change any input above and the page recomputes as you type.

Two things stand out in the table. The price is close to linear in income once other debt is zero, because the housing budget is a fixed share of income and the monthly cost is close to linear in price. And the $500 of debt costs about the same number of dollars of price at every salary, which is why it hurts a lower income so much more in proportion. The one exception is when the smaller price pushes the same down payment over the 20% line, which drops mortgage insurance and gives a little of the price back.

The calculator ranks its own drivers above, in dollars of price per step, for the inputs you entered. The steps are the sizes people actually negotiate in: a quarter point of rate, a hundred dollars of monthly debt, ten thousand dollars of down payment or income. Read the list as what one move buys, not as a league table; a different step size would reorder it. The levers themselves behave the same way in every scenario.

The rate changes the payment on every dollar of the loan for the life of the loan, so a quarter point at the default inputs moves the price by thousands of dollars. Buying down the rate, or waiting for a lower one, changes what you can afford more than most other things a buyer controls.

Other monthly debt is the lever most people underestimate. A $100 monthly payment is not $100 of house; it is $100 of housing budget, and at today's rates a dollar of monthly budget carries well over a hundred dollars of price. Paying off a small loan before applying can add more to the answer than a year of saving for the down payment.

The down payment is worth a little less than a dollar of price per dollar saved, almost everywhere: 0.903 at the $40,000 default and 0.897 once the loan is comfortably under 80% of the price. The dollar buys its own dollar of price and stops paying interest, but property tax and insurance scale with the price too, so the budget it frees carries a little less house than the dollar itself did.

The exception is the reason 20% is a number everyone knows. Between $91,500 and $97,500 down at these inputs, the budget can no longer carry a bigger loan and the price is simply whatever the down payment is 20% of. Each dollar of down payment there moves the price by $5. That is the $92,000 example above: it affords $460,000, and $1,000 more down would afford $465,000. Above the band the loan stops being the binding constraint and the slope drops back under one.

Property tax and HOA dues matter more than their size suggests, because they are monthly costs that never amortize away and, in the case of tax, grow with the price. A neighborhood with a higher effective tax rate buys less house for the same payment, which is the arithmetic behind the advice to compare total monthly cost, not list price.

Income moves the answer the most per ten thousand dollars, because the housing budget is a fixed share of it and everything else is carved out of that share. It is also the input a buyer can change least on a closing timeline, which is why the other four get the negotiation.

The ratio rule is the start of an approval, not the end. A lender also looks at your credit score, which sets the rate you are actually offered and the ratio you are allowed. It looks at reserves, the months of payments you still have in the bank after closing. It looks at the stability of the income, the appraisal of the specific home, and loan limits that cap a conforming mortgage by county. None of that is in the model, and all of it can move the real number in either direction.

The defaults are national. Property tax in particular varies by an order of magnitude between states, and homeowners insurance has been rising fastest in the regions with the most weather risk. If you know the county, replace the tax rate with its effective rate and the insurance with a real quote; those two fields are where the national default is most likely to be wrong for you.

And the answer is a ceiling, not a target. The ratio says what a lender will allow; it says nothing about what leaves room for retirement savings, childcare, or a job change. Many people choose to borrow well under the number the rule permits, and the 28/36 option under the number is a reasonable picture of what that looks like.

This calculator is built to be used without a browser. Every input is a query parameter on this page, and the same parameters on the JSON twin return the complete answer as a document.

GET /tools/house-affordability.json?income=150000&down=50000

The response carries inputs after parsing and clamping, result with the maximum price, loan, ratios, monthly breakdown, and upfront cash to close, plus sensitivity tables by debt-to-income limit, rate, and term, drivers ranked by effect with a plain sentence each, assumptions that say for every field whether you supplied it and name the source when the default came from one, sources with a URL and an as-of date for each source the tool cites, which is an empty list on the calculators whose every default is an example input rather than a published figure, warnings, a disclaimer, and in tool the canonicalUrl and jsonUrl that carry only your non-default parameters. The canonical URL is the answer's permanent address; use it when you cite the number.

Parameters, all optional, in any order:

• income ($), default $100,000.
• debts ($ per month), default $0 per month.
• down ($), default $40,000.
• rate (%), default 6.65%, from Freddie Mac Primary Mortgage Market Survey.
• term (years), default 30 years.
• taxRate (%), default 0.888%, from NAHB Eye On Housing, Property Taxes by State, 2024 (American Community Survey).
• insurance ($), default $1,600, from NAIC, Examining Homeowner Property Insurance Market Dynamics, 2018 to 2024.
• hoa ($ per month), default $0 per month.
• pmiRate (%), default 0.6%, from Freddie Mac, Breaking down PMI.
• closingRate (%), default 3.5%, from Freddie Mac, What are closing costs and how much will I pay?.
• dti (%), default 36%, from Fannie Mae Selling Guide B3-6-02, Debt-to-Income Ratios.
• frontDti (%), default off.

Values accept plain numbers and loose human formats such as 100k, $100,000, or 6.5%. Unknown parameters are ignored, values outside a field's range are clamped and reported in warnings, and the endpoint never fails on bad input. Responses are cacheable for a day; the defaults change when their sources publish, and tool.version changes when the method does.

• Freddie Mac Primary Mortgage Market Survey, as of 2026-08-20. 30-year fixed-rate mortgage average 6.65%; 15-year 5.95%.
• NAHB Eye On Housing, Property Taxes by State, 2024 (American Community Survey), as of 2025-11-26. National effective property tax rate $8.88 per $1,000 of home value (0.888%); average annual bill $4,271. The article publishes no median, so none is quoted here.
• NAIC, Examining Homeowner Property Insurance Market Dynamics, 2018 to 2024, as of 2026-07-31. 2024 average homeowners premium per policy: $1,600 countrywide; Northeast $1,396, Midwest $1,476, West $1,600, Southeast $1,818.
• Fannie Mae Selling Guide B3-6-02, Debt-to-Income Ratios, as of 2025-04-02. Manually underwritten loans: maximum total DTI 36%, up to 45% with credit score and reserve requirements. Desktop Underwriter: maximum 50%.
• Freddie Mac, Breaking down PMI, as of 2026-08-21. Private mortgage insurance typically costs $30 to $70 per month for every $100,000 borrowed (0.36% to 0.84% of the loan per year). Required on conventional loans with less than 20% down.
• Freddie Mac, What are closing costs and how much will I pay?, as of 2026-02-26. Closing costs typically run 2% to 5% of the home purchase price, paid in addition to the down payment.

Default values on this page: rate 6.65% (Freddie Mac Primary Mortgage Market Survey), property tax 0.888% of value (NAHB Eye On Housing, Property Taxes by State, 2024 (American Community Survey)), insurance $1,600 a year (NAIC, Examining Homeowner Property Insurance Market Dynamics, 2018 to 2024), mortgage insurance 0.6% of the loan (Freddie Mac, Breaking down PMI), closing costs 3.5% of the price (Freddie Mac, What are closing costs and how much will I pay?).

Carlo is a personal finance agent. It knows your accounts, debts, and goals, so instead of a ratio on an example salary it can tell you what a given home does to your savings rate, your taxes, and the other things you are working toward. Text it the question.

ask carlo anything(415) 376-5678