{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"mortgage-affordability"},"result":{"entity_type":"calculator","id":"mortgage-affordability","calculator_id":"mortgage-affordability","canonical_url":"https://tttkmbb.com/investing/mortgage-affordability","name":"Mortgage Affordability Calculator","title":"Mortgage Affordability Calculator – Maximum Loan and Home Price from Income and 28/36 Ratios","category":"investing","category_name":"Investing & Real Estate","tool_name":"calculate_mortgage_affordability","featured_mcp_tool":false,"description":"Applies the front-end (housing) and back-end (total debt) debt-to-income limits to gross income, subtracts taxes and insurance to get the affordable principal-and-interest payment, and converts it into a maximum loan amount and home price for the given rate and term.","use_when":"You want to know how much house or mortgage an income supports under standard lender ratios, before applying for a loan.","do_not_use_when":"You already have a loan amount and want its payment (use mortgage-payment) or want to check ratios for an existing payment (use debt-to-income). Lender rules vary; informational only, not financial advice.","inputs":[{"name":"annual_gross_income","label":"Annual gross income","type":"number","required":true,"max":1000000000,"exclusive_min":0,"description":"Household income before taxes, per year.","example":90000},{"name":"monthly_debt_payments","label":"Monthly debt payments","type":"number","required":false,"default":0,"min":0,"max":10000000,"description":"Minimum payments on car loans, student loans, credit cards and other debts (excluding the new housing payment).","example":500},{"name":"down_payment","label":"Down payment","type":"number","required":false,"default":0,"min":0,"max":10000000000,"description":"Cash available for the down payment; added to the loan to get the home price.","example":50000},{"name":"interest_rate_percent","label":"Interest rate","type":"number","unit":"% per year","required":true,"min":0,"max":30,"description":"Annual mortgage rate; the monthly rate is rate/12.","example":6},{"name":"term_years","label":"Loan term","type":"number","unit":"years","required":false,"default":30,"min":1,"max":40,"description":"Amortization period in years.","example":30},{"name":"front_end_ratio_percent","label":"Front-end ratio","type":"number","unit":"%","required":false,"default":28,"min":1,"max":100,"description":"Maximum housing payment (principal, interest, taxes, insurance) as a percent of gross monthly income.","example":28},{"name":"back_end_ratio_percent","label":"Back-end ratio","type":"number","unit":"%","required":false,"default":36,"min":1,"max":100,"description":"Maximum total debt payments including housing as a percent of gross monthly income.","example":36},{"name":"monthly_taxes_insurance","label":"Monthly taxes and insurance","type":"number","required":false,"default":0,"min":0,"max":1000000,"description":"Property tax, homeowner's insurance, HOA and mortgage insurance per month, which count toward the housing payment.","example":300}],"outputs":[{"name":"front_end_limit","label":"Front-end housing limit","type":"number","decimals":2,"description":"monthly income × front_end_ratio."},{"name":"back_end_limit","label":"Back-end housing limit","type":"number","decimals":2,"description":"monthly income × back_end_ratio − monthly_debt_payments."},{"name":"max_monthly_housing_payment","label":"Maximum monthly housing payment","type":"number","decimals":2,"description":"The lower of the two limits (PITI)."},{"name":"limiting_ratio","label":"Binding constraint","type":"string","decimals":4,"description":"Which ratio sets the limit."},{"name":"max_principal_and_interest","label":"Maximum principal and interest","type":"number","decimals":2,"description":"max_monthly_housing_payment − monthly_taxes_insurance."},{"name":"max_loan_amount","label":"Maximum loan amount","type":"number","decimals":2,"description":"P&I × (1 − (1 + i)^−n) / i with i = rate/12 and n = term × 12."},{"name":"max_home_price","label":"Maximum home price","type":"number","decimals":2,"description":"max_loan_amount + down_payment."},{"name":"income_multiple","label":"Loan-to-income multiple","type":"number","decimals":2,"description":"max_loan_amount / annual_gross_income."}],"input_schema":{"type":"object","properties":{"annual_gross_income":{"description":"Household income before taxes, per year.","type":"number","maximum":1000000000,"exclusiveMinimum":0,"examples":[90000]},"monthly_debt_payments":{"description":"Minimum payments on car loans, student loans, credit cards and other debts (excluding the new housing payment).","type":"number","minimum":0,"maximum":10000000,"default":0,"examples":[500]},"down_payment":{"description":"Cash available for the down payment; added to the loan to get the home price.","type":"number","minimum":0,"maximum":10000000000,"default":0,"examples":[50000]},"interest_rate_percent":{"description":"Annual mortgage rate; the monthly rate is rate/12. Unit: % per year.","type":"number","minimum":0,"maximum":30,"examples":[6],"x-unit":"% per year"},"term_years":{"description":"Amortization period in years. Unit: years.","type":"number","minimum":1,"maximum":40,"default":30,"examples":[30],"x-unit":"years"},"front_end_ratio_percent":{"description":"Maximum housing payment (principal, interest, taxes, insurance) as a percent of gross monthly income. Unit: %.","type":"number","minimum":1,"maximum":100,"default":28,"examples":[28],"x-unit":"%"},"back_end_ratio_percent":{"description":"Maximum total debt payments including housing as a percent of gross monthly income. Unit: %.","type":"number","minimum":1,"maximum":100,"default":36,"examples":[36],"x-unit":"%"},"monthly_taxes_insurance":{"description":"Property tax, homeowner's insurance, HOA and mortgage insurance per month, which count toward the housing payment.","type":"number","minimum":0,"maximum":1000000,"default":0,"examples":[300]}},"additionalProperties":false,"required":["annual_gross_income","interest_rate_percent"]},"output_schema":{"type":"object","properties":{"front_end_limit":{"description":"monthly income × front_end_ratio.","type":"number"},"back_end_limit":{"description":"monthly income × back_end_ratio − monthly_debt_payments.","type":"number"},"max_monthly_housing_payment":{"description":"The lower of the two limits (PITI).","type":"number"},"limiting_ratio":{"description":"Which ratio sets the limit.","type":"string"},"max_principal_and_interest":{"description":"max_monthly_housing_payment − monthly_taxes_insurance.","type":"number"},"max_loan_amount":{"description":"P&I × (1 − (1 + i)^−n) / i with i = rate/12 and n = term × 12.","type":"number"},"max_home_price":{"description":"max_loan_amount + down_payment.","type":"number"},"income_multiple":{"description":"max_loan_amount / annual_gross_income.","type":"number"}}},"formula":"monthly_income = annual_gross_income / 12; housing = min(monthly_income × front_end/100, monthly_income × back_end/100 − monthly_debt_payments); P&I = housing − monthly_taxes_insurance; max_loan = P&I × (1 − (1 + r/12)^−(12·term)) / (r/12); max_price = max_loan + down_payment","method":"Classic 28/36 qualifying ratios (front-end housing, back-end total debt) as used in conventional US underwriting; actual approvals also depend on credit score, reserves, loan program and the appraisal. Informational mathematics only; not financial advice.","sources":[{"name":"CFPB – What is a debt-to-income ratio?","url":"https://www.consumerfinance.gov/ask-cfpb/what-is-a-debt-to-income-ratio-en-1791/","type":"government","retrieved_at":"2026-09-24"},{"name":"Fannie Mae Selling Guide B3-6-02 – Debt-to-Income Ratios (36 % maximum for manual underwriting)","url":"https://selling-guide.fanniemae.com/sel/b3-6-02/debt-income-ratios","type":"standard","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"90,000 income, 500 debts, 50,000 down, 6 %, 30 years, 300 taxes/insurance","inputs":{"annual_gross_income":90000,"monthly_debt_payments":500,"down_payment":50000,"interest_rate_percent":6,"term_years":30,"monthly_taxes_insurance":300},"expected":{"front_end_limit":2100,"back_end_limit":2200,"max_monthly_housing_payment":2100,"limiting_ratio":"Front-end ratio (28 % of gross income)","max_principal_and_interest":1800,"max_loan_amount":300224.91,"max_home_price":350224.91,"income_multiple":3.34},"url":"https://tttkmbb.com/api/v1/calculate/mortgage-affordability?annual_gross_income=90000&monthly_debt_payments=500&down_payment=50000&interest_rate_percent=6&term_years=30&monthly_taxes_insurance=300"},{"name":"120,000 income, 1,200 debts, 80,000 down, 5.5 %, 25 years, 450 taxes/insurance","inputs":{"annual_gross_income":120000,"monthly_debt_payments":1200,"down_payment":80000,"interest_rate_percent":5.5,"term_years":25,"monthly_taxes_insurance":450},"expected":{"front_end_limit":2800,"back_end_limit":2400,"max_monthly_housing_payment":2400,"limiting_ratio":"Back-end ratio (36 % of gross income minus other debts)","max_principal_and_interest":1950,"max_loan_amount":317544.33,"max_home_price":397544.33},"url":"https://tttkmbb.com/api/v1/calculate/mortgage-affordability?annual_gross_income=120000&monthly_debt_payments=1200&down_payment=80000&interest_rate_percent=5.5&term_years=25&monthly_taxes_insurance=450"}],"faq":[{"q":"Where do 28 and 36 come from?","a":"They are the traditional conventional-mortgage guidelines: housing costs up to 28 % of gross income and all debt up to 36 %. Fannie Mae allows up to 36 % (45 % with compensating factors) for manually underwritten loans and up to 50 % through automated underwriting."},{"q":"Is the result what a lender will approve?","a":"No. It is the payment the ratios allow; lenders also weigh credit history, employment, cash reserves and the property, and some use different ratios."}],"tags":["mortgage affordability","how much house can i afford","28/36 rule","debt to income","maximum loan amount","home buying budget"],"related":[{"calculator_id":"mortgage-payment","reason":"Full payment for a chosen loan amount."},{"calculator_id":"debt-to-income","reason":"Check the ratios for an existing payment."},{"calculator_id":"loan-payment","reason":"Level payment on any amortizing loan."}],"links":{"html":"https://tttkmbb.com/investing/mortgage-affordability","markdown":"https://tttkmbb.com/investing/mortgage-affordability.md","json":"https://tttkmbb.com/investing/mortgage-affordability.json","api":"https://tttkmbb.com/api/v1/calculate/mortgage-affordability","schema":"https://tttkmbb.com/api/v1/calculators/mortgage-affordability","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T03:50:06Z"}