Mortgage Affordability Calculator Widget

Add a home affordability calculator based on the 28/36 rule lenders use. Readers enter income, existing debt payments, down payment and rate and see the highest price the rule allows, the payment it means and both debt-to-income ratios.

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<iframe src="https://a2z.tools/embed/w/mortgage-affordability-calculator" title="Mortgage Affordability Calculator by A2Z Tools" width="100%" height="820" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>

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How it works

The housing budget is the smaller of two limits: the front-end limit (housing costs no more than 28% of gross monthly income) and the back-end limit (housing plus other debt payments no more than 36%). The monthly cost of a home is the mortgage payment on the price minus the down payment plus property tax and insurance, estimated as a percentage of the price. Setting that cost equal to the budget and solving gives the highest price. Both limits are editable for lenders or loan types that use different ratios.

Calculation method

  • G = gross annual income / 12; D = down payment; t = tax + insurance as % of price a year
  • Housing budget H = min(G x front%, G x back% - other monthly debt payments)
  • Payment factor k = r / (1 - (1 + r)^-n), r = annual rate / 12 / 100, n = years x 12 (k = 1 / n at 0%)
  • Monthly cost of a price X = (X - D) x k + X x t / 12
  • Highest price X = (H + D x k) / (k + t / 12); if X would need no loan, X = H / (t / 12) capped at D
  • Nothing is rounded during the calculation; price and loan are displayed to whole currency units, the monthly payment to 2 decimals, ratios to 1 decimal

Worked examples

Front-end limit binds

Inputs: Income 120,000 a year, other debts 500 a month, down payment 60,000, 6.5% for 30 years, tax + insurance 1.5% of price

Result: Affordable price 419,941; loan 359,941; housing payment 2,800.00 (principal and interest 2,275 + tax and insurance 525); ratios 28% / 33%

Monthly income is 10,000, so housing may take 2,800 while the back-end room is 3,600 - 500 = 3,100. The smaller 2,800 sets the price.

Back-end limit binds

Inputs: Income 90,000 a year, other debts 900 a month, down payment 30,000, 7% for 30 years, tax + insurance 1.5%

Result: Affordable price 253,016; loan 223,016; housing payment 1,800.00; ratios 24% / 36%

Monthly income is 7,500: 28% allows 2,100 but 36% less the 900 of debts leaves only 1,800, so existing debt caps the purchase.

A guideline estimate, not a loan offer or financial advice. Lenders apply their own criteria.

Limitations

  • Uses gross income and the ratios you enter; it does not know any lender's actual debt-to-income ceiling or credit-score rules.
  • HOA dues, PMI and closing costs are not included in the housing budget - add HOA or PMI to 'other debt payments' if you want them counted.
  • Property tax and insurance are modelled as a flat percentage of the price, which understates them where a fixed insurance premium dominates on cheaper homes.

Where publishers use it

  • Estate agents' first-time-buyer guides
  • Mortgage brokers qualifying leads before a call
  • Relocation and cost-of-living articles comparing cities
  • Personal-finance posts explaining debt-to-income ratios
  • Credit-union and employer financial-wellness portals preparing members for pre-approval

Questions

What is the 28/36 rule?

A long-standing rule of thumb, not a regulation: spend no more than 28% of gross monthly income on housing (mortgage, property tax, insurance) and no more than 36% on all debt payments including housing. Individual lenders and loan programmes set their own maximum ratios, so both limits are editable.

Is this the amount a lender will approve?

Not necessarily. Underwriters also look at credit score, cash reserves, employment history and the loan type, and may approve more or less.

Why does adding a car payment lower the price so much?

Other debts count against the back-end limit. Once that limit is the tighter one, every extra dollar of monthly debt removes a dollar from the housing budget - at 6.5% over 30 years with tax and insurance at 1.5% of the price, 100 a month of car payment cuts about 13,200 from the affordable price.

How should I estimate tax and insurance?

Take the annual property tax from the county assessor or a comparable listing, add a homeowners-insurance quote, and divide by the price. Where the result lands varies greatly by county, so avoid borrowing a figure from another state.

Which limit is holding my price down?

The hint under the price says whether the front-end (housing) or back-end (total debt) rule binds. With no other debts the front-end limit always binds; paying off a card or car loan only raises the price once the back-end limit is the tighter one.

Sources

  1. What is a debt-to-income ratio? - Consumer Financial Protection Bureau (US) . Definition of DTI as monthly debt payments divided by gross monthly income. The CFPB page does not set 28% or 36%; those are an industry rule of thumb.

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A2Z Tools Mortgage Affordability Calculator
https://a2z.tools/embed/mortgage-affordability-calculator

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