How This House Affordability Calculator Works
Choose a Calculation Mode and Enter the Inputs
Both modes use these shared inputs:
- Down payment ($)
- Interest rate (annual %)
- Loan term (years)
- Property tax rate (annual %, optional)
- Homeowners insurance ($/year, optional)
- HOA / condo fees ($/month, optional)
In income mode, also enter Gross annual income ($), Other recurring monthly debts ($, optional), Front-end DTI threshold (% of income, housing only), and Back-end DTI threshold (% of income, housing + all debts). In payment mode, enter Target total monthly housing payment ($) instead. Blank optional fields are treated as zero.
How the Calculation Works
In income mode, the calculator converts annual income to monthly income, then calculates a front-end housing limit and a back-end housing limit after other monthly debts. The lower limit becomes the target monthly housing payment. Payment mode uses the target payment you enter directly.
Front-end limit = Gross monthly income x (Front-end DTI % / 100)
Back-end limit for housing = (Gross monthly income x (Back-end DTI % / 100)) - Other monthly debts
The lower limit becomes the target payment:
Target monthly housing payment = min(Front-end limit, Back-end limit for housing)
In payment mode, the target monthly housing payment is the amount you enter.
The calculator then searches by bisection for a home price where principal & interest, monthly property tax, monthly insurance, and HOA fees equal that target:
Loan amount = Price - Down payment
Monthly rate r = Annual rate / 100 / 12
P&I = Loan amount x r(1 + r)^n / ((1 + r)^n - 1)
Here, n is the number of monthly payments. At a 0% interest rate, the script uses Loan amount / number of payments instead of the formula with r in the denominator.
Read, Copy, or Download the Result
- Fixed-rate, fully amortizing loan: the loan is assumed to have a constant interest rate and equal monthly principal & interest payments over the full term.
- You set the DTI thresholds: the front-end and back-end percentages are values you choose, not a fixed lender rule or approval requirement.
- Property tax and insurance are ongoing estimates: property tax is calculated as a percentage of the estimated home price per year; insurance is a flat annual dollar figure you provide. Neither reflects a specific assessment, policy quote, or jurisdiction.
- HOA/condo fees are flat and monthly: entered directly, and assumed not to change over time.
- Down payment is fixed in dollars: it does not scale with the solved price; the loan amount is simply price minus down payment.
- No closing costs, PMI, or one-time fees: only recurring monthly housing costs are included in the payment used to solve for price.
The result displays the estimated affordable home price, loan amount, monthly principal & interest (P&I), and total estimated monthly housing cost (PITI + HOA). Income mode also displays the front-end and back-end DTI percentages achieved with their limits. Compare those percentages with the limits you entered. The formula and assumptions table lists the main assumptions and calculated values.
Use Copy result for a plain-text summary, or Download result (.txt) to create house-affordability-result.txt.
Limits, Validation, and Scope
The calculator requires an interest rate from 0 to 30% and a whole-number loan term from 1 to 50 years. Down payment, property tax rate, insurance, and HOA fees cannot be negative when entered. Gross annual income must be greater than 0 in income mode, and other recurring monthly debts cannot be negative when entered.
The calculation script accepts DTI thresholds greater than 0 and up to 100. The visible fields show a minimum of 1, but values such as 0.5 are accepted by the script. The visible property-tax field shows a maximum of 10, but the calculation script checks only that the entered rate is not negative.
A target payment must be greater than 0. It can fail when taxes, insurance, and HOA fees already exceed that payment at a home price equal to the down payment, where the calculated loan is zero.
The estimate does not check credit, employment, or assets; apply lender-specific underwriting rules; or determine approval. It excludes closing costs, PMI, and other one-time purchase costs. Treat it as a calculation based on the figures and thresholds you enter, not as a pre-approval, lender quote, guarantee, or personalized financial advice.
How to Use the House Affordability Calculator
- Choose Estimate price from income & DTI limits or Estimate price from a target monthly payment.
- Enter your loan and home cost details: down payment, interest rate, loan term, property tax rate, insurance, and HOA fees.
- In income mode, enter your gross annual income, other monthly debts, and the front-end and back-end DTI thresholds you want to use.
- In payment mode, enter the total monthly housing payment you're targeting.
- Select Calculate to see the estimate.
- Select Copy result or Download result (.txt).
Privacy and Calculator Input Handling
The calculation logic processes the calculator values in the browser, and the calculator workflow does not require an account. This statement applies to the calculator's input handling only; it does not describe all data handling on the page.
Frequently Asked Questions
How does the House Affordability Calculator estimate a home price?
It works out the maximum monthly housing payment your gross income can support using two debt-to-income thresholds you choose: a front-end limit (housing cost only) and a back-end limit (housing cost plus all other recurring debts). The lower of the two resulting housing-payment limits is used as the target monthly payment, and the calculator solves for the home price whose principal & interest, property taxes, insurance, and HOA add up to that payment, given your down payment, rate, and term.
What is the difference between the front-end and back-end debt-to-income ratio?
The front-end ratio compares only the estimated monthly housing cost (principal & interest, taxes, insurance, and HOA) to gross monthly income. The back-end ratio compares total monthly debt - housing cost plus your other recurring debts such as car loans, student loans, or credit cards - to gross monthly income. This tool lets you set both thresholds yourself rather than assuming a fixed lender rule.
What does the reverse mode (target monthly payment) do?
Reverse mode skips the income and debt-to-income inputs and instead lets you enter a target total monthly housing payment directly. The calculator solves for the home price whose principal & interest, property taxes, insurance, and HOA add up to that payment, given your down payment, rate, and term - the same underlying price-solving formula as the income-based mode.
Does this tool determine loan approval or use lender underwriting rules?
No. This is a transparent mathematical estimate based only on the numbers and thresholds you enter. It does not check credit, employment, assets, or any lender-specific underwriting rule, and it is not a pre-qualification, pre-approval, or guarantee of what any lender will offer.
Are principal & interest shown separately from the total housing cost?
Yes. The result shows the estimated monthly principal & interest (P&I) payment on its own, and separately shows the total estimated monthly housing cost, which adds property taxes, homeowners insurance, and HOA/condo fees on top of P&I.