House Affordability Calculator — DTI & Price Limits
Find the home price your income, debts and down payment support, with front and back DTI limits, PMI, taxes and cash to close made explicit, free.
A clear path from inputs to results.
Work backwards from your income to the home price it supports: the tool applies front- and back-end debt-to-income limits, reserves room for taxes, insurance and HOA, then converts what is left into a maximum loan and price. A budget mode does the same from a fixed monthly housing number instead of income.
How to use
- Choose income mode (size the price from what you earn) or budget mode (start from a monthly housing number you already have in mind).
- In income mode, enter gross annual income and your other monthly debt payments; pick a DTI preset — conventional 28/36, FHA 31/43, VA 41/41 or an aggressive 45/50.
- Enter the down payment as an amount or a percentage of price, the expected mortgage rate and the term.
- Add annual property tax, annual insurance and monthly HOA; in US mode a PMI rate is applied automatically when the down payment is under 20%.
- Read the results: maximum price, the loan amount, the total monthly payment including PMI, cash to close (down payment plus an estimated 3% in closing costs), and your resulting DTI.
- Scan the equity table to see the balance fall and equity build over the term, and note any flags such as the conforming-limit (jumbo) warning.
The formula
Reference: Inverted annuity-immediate loan sizing (Broverman, Mathematics of Investment and Credit); front- and back-end DTI conventions from US mortgage underwriting (28/36 conventional, 31/43 FHA, 41 VA). Computed with Big.js decimal arithmetic.
Worked example
$120,000 income, conventional 28/36, 20% down
- Gross income $120,000/yr; other monthly debts $500; conventional DTI 28/36; down payment 20%; rate 6.75%; 30-year term; property tax $4,800/yr; insurance $1,500/yr; HOA $0; US region.
- 1
Monthly gross income is $10,000, so the front-end limit allows 28% × $10,000 = $2,800 of housing and the back-end allows 36% × $10,000 − $500 = $3,100; the smaller $2,800 governs. Subtracting the $525 of fixed costs (tax $400.00 plus insurance $125.00) leaves $2,275 for principal, interest and PMI. Inverting the annuity formula at 6.75% over 360 months sizes a loan of $350,756.50, which at 20% down implies a price of $438,445.63. Cash to close is the $87,689.13 down payment plus an estimated 3% closing costs ($13,153.37), or $100,842.49, and the resulting DTI is 33%.
Maximum price about $438,446 (loan $350,756.50); total monthly housing $2,800; cash to close about $100,842; DTI 33%.
Interpreting the result
Which DTI limit binds matters: here the front-end 28% caps you, so paying off the $500 of debts would not raise the price until monthly debts passed about $800 and the back-end became the constraint — past that point, every extra $100 of debt trims roughly $19,300 of buying power at these rates. The cash-to-close figure is often the real barrier, and the equity table shows how slowly principal builds in the early years. Treat the output as a sizing starting point, since lenders also weigh credit, reserves and employment.
Assumptions & limitations
- Closing costs are estimated at a flat 3% of the purchase price, plus UK Stamp Duty estimates or a custom transfer tax in other regions.
- PMI applies in US mode only, when the down payment is a percentage under 20%; it is modeled as a constant monthly charge (rate ÷ 12 × loan).
- Property tax, insurance, HOA and (in UK mode) ground rent and service charge are flat amounts you enter; they are subtracted from the DTI budget before sizing the loan.
- The universal region adds your custom stress percentage to the rate before sizing, to preview a higher-rate environment.
- The result is a sizing estimate, not a pre-approval: credit history, reserves and lender overlays are not modeled.
Frequently asked questions
What do the 28/36 numbers mean?
They are underwriting debt-to-income caps: 28% of gross income for housing costs alone (front-end) and 36% for housing plus all other monthly debts (back-end). The tool computes both budgets and uses the smaller — in the worked example, $2,800 versus $3,100, so the front-end governs. The FHA (31/43), VA (41/41) and aggressive (45/50) presets swap in their own limits.
What happens if I put down less than 20%?
In US mode a monthly PMI charge (your entered rate on the loan, 0.55% by default) is included inside the housing budget, so it eats into what is left for principal and interest. At 10% down on the example, PMI of $150.15 a month cuts the supportable price from $438,445.63 to $364,006.82 — though cash to close drops to $47,320.89.
Why is the total monthly payment higher than the P&I?
The payment that must fit inside your DTI budget covers everything that arrives with the bill: the tool subtracts tax ($400.00), insurance ($125.00) and any HOA or PMI before sizing the loan, then reports them stacked back on. On the example, $2,275 of principal, interest and PMI plus $525 of escrow equals the full $2,800 housing budget.
How much cash do I need beyond the down payment?
The tool adds an estimated 3% of the price for closing costs on top of your down payment: about $13,153 on the $438,446 example, for $100,842.49 of cash to close. In UK mode it also adds the estimated Stamp Duty from its built-in bands, and universal mode accepts a flat transfer-tax amount you enter.
How does a car loan change my buying power?
Only through the back-end limit. The example's $500 of monthly debt still leaves back-end headroom, so it does not bite; at $900 of debts the back-end caps housing at $2,700 and the price falls to about $419,173. Once debts pass roughly $800 a month, every extra $100 costs about $19,300 of price at these rates.
What is the jumbo-loan flag?
When the computed price exceeds the tool's built-in $832,750 conforming limit, it warns that the loan would be jumbo and underwritten more strictly, with heavier reserve expectations. The affordability math itself still runs; the flag is a heads-up that rates, limits and requirements often differ above that line.
Methodology last reviewed 2026-10-06. Results are informational and not financial or engineering advice — see our disclaimer.