House Affordability Calculator

How the House Affordability Calculator works

Use this calculator before comparing mortgage payments, a Debt-to-Income Calculator result, Down Payment Calculator scenarios, or a Rent vs. Buy Calculator estimate. It is useful for testing how income, debts, rates, down payment size, tax assumptions, insurance, PMI, HOA dues, and maintenance can change an illustrative price ceiling. It is not a lender pre-approval, Loan Estimate, underwriting decision, appraisal, property tax bill, insurance quote, or advice to buy a particular home.

The calculator first computes monthly income as annualHouseholdIncome / 12. For income-DTI mode, frontEndBudget equals monthly income times the selected front-end ratio, while backEndBudget equals monthly income times the selected back-end ratio minus monthlyDebtPayment. The usable housing budget is Math.min(frontEndBudget, backEndBudget), floored at zero. For fixed-budget mode, the calculator uses monthlyHousingBudget directly. The mortgage payment factor uses annualRate / 100 / 12 over termYears * 12 payments. The down payment share is downPaymentPercent / 100, and PMI is included only when downPaymentPercent < 20. HOA is converted with hoaPerYear / 12. After adding the per-dollar costs for loan payment, tax, insurance, PMI, and maintenance, maxHomePrice is solved as (monthlyHousingBudget - monthlyHoa) / perDollarMonthlyCost. The calculator then reports loan amount, down payment, monthly cost parts, frontEndDti, and backEndDti.

House Affordability Calculator formula

This formula page covers the app's House Affordability Calculator: income-DTI and fixed-budget home-price solves, selected front-end and back-end DTI limits, existing monthly debt, mortgage principal-and-interest, property tax, home insurance, PMI, HOA, maintenance, and output DTI ratios. It does not calculate lender pre-approval, an Ability-to-Repay or Qualified Mortgage determination, FHA or VA underwriting, a Loan Estimate, closing costs, tax bills, insurance quotes, HOA statements, rate locks, or personalised borrowing advice.

Step by step

1. Read the affordability mode, annual household income, monthly debt payment, fixed monthly housing budget, rate, term, down payment, property tax, insurance, PMI, HOA, maintenance, DTI profile, and custom DTI ratios.
2. Resolve the selected DTI profile into front-end and back-end ratio limits. The conventional, FHA, VA, and custom labels are app inputs for planning math, not complete underwriting rules.
3. Convert annual household income to monthly income by dividing by 12.
4. In income-DTI mode, calculate the front-end budget from monthly income times the front-end ratio, then calculate the back-end budget from monthly income times the back-end ratio minus existing monthly debt.
5. Use the lower of the front-end and back-end budgets for income-DTI mode, clamped at 0 so high existing debt cannot create a negative housing budget.
6. In fixed-budget mode, use the entered monthly housing budget directly instead of the income-DTI profile for the home-price solve.
7. Convert the annual rate to a monthly rate, multiply term years by 12, and calculate the mortgage payment factor. If the monthly rate is 0, use 1 divided by the payment count.
8. Convert down payment percent to a loan share. Activate PMI only when the down payment is below 20 percent.
9. Convert HOA to a monthly fixed cost, then calculate per-dollar monthly cost from principal-and-interest, property tax, insurance, maintenance, and active PMI percentages.
10. Subtract monthly HOA from the selected housing budget and divide the remaining budget by per-dollar monthly cost to solve the maximum home price. If per-dollar monthly cost is 0 or less, return 0 for the price.
11. Calculate loan amount, down payment amount, monthly principal-and-interest, monthly property tax, monthly insurance, monthly PMI, monthly HOA, and monthly maintenance from the solved price.
12. Add the payment components to get monthly housing payment, then calculate front-end DTI and back-end DTI from monthly income. If monthly income is 0, both displayed DTI outputs return 0.
13. Round currency and percentage outputs to two decimals after the full-precision solve.
14. Use CFPB, Regulation Z section 1026.43, Fannie Mae, HUD FHA, VA, lender, local tax, insurance, HOA, legal, or local regulator sources before adding underwriting, disclosure, approval, FHA, VA, product-specific, tax, insurance, HOA, legal, or jurisdiction-specific claims.

Worked example

Income-DTI and fixed-budget examples: conventional 20 percent down versus PMI

The examples use the app's package fixtures so the numbers match the calculator implementation rather than a generic affordability rule.

1. Income-DTI fixture: $120,000 of annual household income becomes $10,000.00 per month.
2. The conventional profile uses 28 percent front-end and 36 percent back-end inputs. Front-end budget is $2,800.00. Back-end budget is $2,950.00 after subtracting $650.00 of existing monthly debt, so the selected housing budget is $2,800.00.
3. With a 6.5 percent rate, 30-year term, 20 percent down payment, 1.2 percent tax, 0.35 percent insurance, $1,200 annual HOA, and 1 percent maintenance, the solved maximum home price is $375,963.71.
4. That price produces a $300,770.97 loan amount and a $75,192.74 down payment amount.
5. The monthly housing payment is $2,800.00: $1,901.08 principal and interest, $375.96 property tax, $109.66 insurance, $0.00 PMI, $100.00 HOA, and $313.30 maintenance.
6. Displayed DTI ratios are 28.00 percent front-end and 34.50 percent back-end.
7. Fixed-budget-with-PMI fixture: $90,000 income becomes $7,500.00 monthly income, but fixed-budget mode uses the entered $2,400.00 monthly housing budget instead of the custom 32/40 DTI budget.
8. With a 6 percent rate, 30-year term, 10 percent down payment, 1.1 percent tax, 0.4 percent insurance, 0.55 percent PMI, $900 annual HOA, and 0.8 percent maintenance, the solved maximum home price is $300,966.14.
9. That price produces a $270,869.53 loan amount, a $30,096.61 down payment amount, and $124.15 of monthly PMI because the down payment is below 20 percent.
10. The fixed-budget monthly housing payment is $2,400.00: $1,624.00 principal and interest, $275.89 property tax, $100.32 insurance, $124.15 PMI, $75.00 HOA, and $200.64 maintenance.
11. Displayed DTI ratios for the fixed-budget fixture are 32.00 percent front-end and 37.33 percent back-end.
12. If existing monthly debt pushes the back-end budget below 0, income-DTI mode clamps the selected housing budget at 0. If monthly HOA is greater than the selected housing budget, the solved home price also clamps at 0.
13. A 100 percent down payment can make the loan share 0, but tax, insurance, maintenance, and HOA assumptions can still affect the solve. If every per-dollar cost is 0, the app returns 0 instead of dividing by zero.
14. Scoped independent comparator checks pass 3 of 4 scoped strict scenarios. The FHA less-than-20-percent-down replay remains a semantic mismatch because the independent comparator appears to include FHA-specific mortgage-insurance or upfront-premium assumptions that this app does not expose as inputs.

The examples show how the app turns entered assumptions into a maximum home-price estimate and payment breakdown. They do not show whether any lender, FHA, VA, insurer, tax authority, HOA, or property-specific review would accept the scenario.

Assumptions and what this calculator ignores

Geographic scope: works globally. The math is currency-agnostic, so enter amounts in your own currency; local taxes, fees, and product rules are not included.

• The conventional, FHA, VA, and custom DTI profiles are calculator assumptions used for education. They do not replace a lender's full underwriting, compensating-factor review, residual-income review, program eligibility rules, or official ability-to-repay analysis.
• Property tax, home insurance, PMI, HOA, and maintenance are simplified inputs. The estimate does not include closing costs, cash reserves, rate locks, escrow changes, special assessments, local tax exemptions, insurance underwriting, or property-specific HOA documents.
• The implementation is checked with deterministic fixtures and internal independent comparator checks. Official-source boundaries remain important for lending disclosures and program rules, including CFPB mortgage materials, Regulation Z section 1026.43, Fannie Mae guidance, HUD FHA policy, VA guidance, and local tax authorities. Results are educational estimates, not financial, tax, legal, lending, mortgage, regulatory, or personalised advice.

What this formula does not include

• The result is not a lender pre-approval, mortgage approval, loan offer, Ability-to-Repay determination, Qualified Mortgage determination, FHA decision, VA decision, legal conclusion, or personalised borrowing advice.
• The calculator uses only entered values. It does not verify income, employment, assets, debts, credit reports, credit score, reserves, property eligibility, appraisal value, title, insurance availability, tax records, HOA documents, or occupancy.
• DTI profile labels are planning inputs for this formula. They do not reproduce current conventional, FHA, VA, automated-underwriting, manual-underwriting, compensating-factor, residual-income, reserve, credit-score, or lender-overlay rules.
• CFPB ATR/QM materials and Regulation Z section 1026.43 require creditor analysis in covered mortgage contexts, but this app does not implement those legal tests and does not prescribe a universal DTI threshold.
• The PMI branch is a simplified annual-rate input that turns on below 20 percent down. It does not model FHA MIP, VA funding fees, upfront mortgage-insurance premiums, borrower-paid versus lender-paid PMI, cancellation rules, or product-specific mortgage-insurance schedules.
• Property tax, homeowners insurance, maintenance, and HOA or co-op fees are entered assumptions. The app does not look up local tax assessments, insurance quotes, flood or hazard coverage, special assessments, condo dues, co-op rules, utility costs, repairs, or escrow changes.
• Closing costs, cash needed at closing, discount points, lender credits, prepaid items, transfer taxes, title fees, appraisal fees, inspection costs, cash reserves, rate locks, and future rate changes are not included in the home-price solve.
• The independent comparator reports closing-cost and cash-at-closing rows that this app intentionally does not expose; its income-DTI form also has an implicit maintenance assumption and automatic PMI behavior that differ from this app's explicit inputs.
• If monthly income is 0, the displayed DTI ratios return 0 to keep the calculator stable. That is a divide-by-zero guard, not evidence that the payment is affordable.
• The result is an educational estimate from entered assumptions, not financial, tax, legal, lending, insurance, housing, consumer-rights, regulated, or personalised advice.

Common mistakes to avoid

• Treating the maximum home price as an approval amount or a recommended purchase price. It is only an estimate from the inputs shown on the page.
• Mixing units, such as entering annual HOA dues as monthly dues, property tax dollars as a percentage, or debts that are not monthly obligations.
• Assuming the profile label sets official program limits. PMI, tax, insurance, HOA, credit, assets, reserves, location, and lender overlays can all change a real lending decision.

Key terms

Income-DTI mode

A solve mode that derives the housing budget from income, existing monthly debts, and selected debt-to-income ratios. It applies the lower of the front-end housing budget and back-end debt budget before solving for home price.

Fixed-budget mode

A solve mode that uses the monthly housing budget entered in the calculator. The app subtracts monthly HOA and then solves the home price that fits loan payment, tax, insurance, PMI, and maintenance assumptions.

Housing DTI

The share of monthly income used by the estimated housing payment. Back-end DTI also includes the existing monthly debt payment entered in the calculator.

Frequently asked questions

Methodology, sources, and disclaimer

This calculator is an original affordability solver converting income-DTI limits or a fixed budget into a maximum home price by charging the full carrying cost - P&I, tax, insurance, PMI under 20 percent down, HOA, and maintenance - per dollar of price, validated by deterministic fixtures. It is not copied from a single source.

Fixtures pin the cost-per-dollar solve, the binding-constraint selection between front-end and back-end limits, and the resulting DTI outputs. The result remains an educational estimate, not a pre-approval or an ability-to-repay determination.

Formula version 2026.05.22-generic-house-affordability. The version marks the calculation logic and validation fixture set used for this estimate.

• CFPB debt-to-income materials should be used before copy defines DTI, gross monthly income, monthly debt payments, and lender-facing consumer education context.
• CFPB mortgage total-monthly-payment materials should be used before copy explains principal and interest, mortgage insurance, escrow, taxes, homeowners insurance, HOA dues, or total mortgage-payment boundaries.
• CFPB Loan Estimate materials should be used before copy discusses loan-offer comparisons, projected payments, five-year costs, lender-controlled costs, taxes and insurance estimates, closing costs, or cash due at closing.
• CFPB Ability-to-Repay and Qualified Mortgage resources plus Regulation Z section 1026.43 should be used before copy discusses mortgage underwriting, income or asset verification, ability-to-repay determinations, monthly DTI, residual income, qualified mortgages, or current no-universal-threshold caveats.
• Fannie Mae Selling Guide B3-6-02 should be used before copy discusses conventional-loan DTI thresholds, manually underwritten limits, Desktop Underwriter limits, reserves, credit-score exceptions, transaction exceptions, or agency-specific conventional mortgage rules.
• HUD FHA Single Family Housing Policy Handbook 4000.1 should be used before copy discusses FHA DTI ratios, mortgage insurance premiums, upfront premiums, compensating factors, TOTAL Mortgage Scorecard, manual underwriting, housing-payment ratios, or FHA product eligibility.
• VA Lenders Handbook Chapter 4 should be used before copy discusses VA income verification, DTI, residual income, shelter expenses, case-by-case underwriting, or VA product eligibility.
• Lender disclosures, local tax authorities, insurers, HOA or co-op documents, agency guides, credit policies, legal sources, and local regulators should be used before copy makes product-specific, approval, rate-lock, tax, insurance, HOA, property, legal, regulated-advice, or jurisdiction-specific claims.

Results are educational estimates, not advice. Read the full disclaimer.

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