2026-09-21 7 min read

Mortgage Affordability Calculator

The home price your income and down payment support for a mortgage. Live calculator with worked steps, charts.

Calculator

Gross Monthly Income

Existing Monthly Debt Payments

Down Payment(%)

Annual Interest Rate(%)

Loan Term(years)

years

Maximum Debt-to-Income Ratio(%)

Property Tax Rate (annual % of value)(%)

Annual Homeowners Insurance

HOA Dues (monthly)

This mortgage basics calculator runs on the standard amortisation model: interest is charged on the outstanding balance each month, and anything extra you enter is applied to principal immediately.

Results

Optimal

Affordable Home Price

$305,786

At 43% back-end DTI with 20% down.

Maximum Loan Amount

$244,629

Monthly Housing Budget

$1,945

29.9% front-end ratio.

Principal & Interest Allowance

$1,795

Comfortable Price at 36% DTI

$228,275

The level most advisers recommend.

Down Payment Required

$61,157

Closing costs come on top.

Back-End DTI at Maximum

43.00%

Front-End Ratio

29.92%

Live results update as you type — currently showing affordable home price of $305,786 on 12 payments a year. Replace the defaults with your own quote for an exact comparison.

Visualizations

Stretch vs Comfortable Budget

305,786Stretch (43%)

228,275Comfortable (36%)

Monthly Housing Budget Split

Principal & interest64%

Taxes0%

Insurance & HOA5%

Other debts30%

Front-End Ratio

29.9%

050

Formula

Working backwards from a payment ceiling: subtract the escrowed costs, size the loan that the remainder services at the rate and term, then add the down payment to reach the affordable price.

Price = (Payment budget − escrow) ÷ (i ÷ (1 − (1 + i)⁻ⁿ)) + down payment

Variables

Symbol	Name	Unit	Description
B	Payment budget	currency	The monthly PITI you can sustain
E	Monthly escrow	currency	Tax + insurance + dues ÷ 12 each
A	Supportable loan	currency	Present value of (B − E) at the rate and term
D	Down payment	currency	Cash applied at closing, plus any concessions

Explanation

This is the price band where the full monthly cost — payment, taxes, insurance, dues — fits inside your target budget at today’s rates, funded by the loan plus your down payment.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Apply the lender DTI ceiling to gross income, then clear existing debts.

Housing = income × DTI − debts

Income:$6,500

Max DTI:43%

Debts:$850

Result: $1,945.00 per month

Step 2

Reserve taxes and insurance before pricing the loan.

P&I budget = housing − taxes − insurance

Result: $1,795.00

Step 3

Discount the payment stream and gross up by the down payment.

Price = [P × (1 − (1 + i)^−n) ÷ i] ÷ (1 − down %)

Result: $305,786

Final Answer

$305,786

Worked Examples

See how the calculator works with different scenarios.

Scenario

The mortgage affordability calculator run on the values above, showing the full calculation path rather than only the answer.

Inputs

Rate:8

Years:30

Income:6500

Calculation

1. Apply the lender DTI ceiling to gross income, then clear existing debts. → $1,945.00 per month 2. Reserve taxes and insurance before pricing the loan. → $1,795.00 3. Discount the payment stream and gross up by the down payment. → $305,786

Result

Affordable Home Price: $305,786

Interpretation

At 43% DTI: housing $1,945.00, P&I $1,795.00, loan $244,629, price $305,786 at 20% down (front-end 29.9%).

Understanding Your Result

Your Result: Affordable Home Price: $305,786

Typical range: Conventional underwriting accepts back-end DTI up to 45%–50% with strong credit, but payment stress rises sharply above 36%.

What This Means

This is the price band where the full monthly cost — payment, taxes, insurance, dues — fits inside your target budget at today’s rates, funded by the loan plus your down payment.

Why It Matters

At 43% DTI: housing $1,945.00, P&I $1,795.00, loan $244,629, price $305,786 at 20% down (front-end 29.9%).

Professional Interpretation

At 43% DTI: housing $1,945.00, P&I $1,795.00, loan $244,629, price $305,786 at 20% down (front-end 29.9%).

How this is calculated

Working backwards from a payment ceiling: subtract the escrowed costs, size the loan that the remainder services at the rate and term, then add the down payment to reach the affordable price.

What drives the result

A ratio compares an obligation with the resource that supports it. Debt-to-income compares payments with gross income, loan-to-value compares the loan with collateral, and debt-service-coverage compares net operating income with annual debt service. Each has a conventional threshold, and crossing one usually means a smaller loan, a co-borrower, or a decline.

Recommendations

•Buy at the comfortable figure; the stretch number is an approval ceiling, not advice.
•Recalculate with the actual county tax rate — it moves the answer more than a rate quote does.

Educational Content

Introduction

Lenders qualify borrowers on ratios, not on intuition: how much of your income is committed to debt, how much collateral backs the loan, and whether the income the asset produces covers its debt service. These calculators put the same numbers a credit officer would use in your hands before you apply.

Concept Explanation

Applications

▸Pre-qualifying yourself before a lender runs a credit check

▸Sizing a purchase so the payment fits a target ratio

▸Testing how paying off one debt changes your borrowing power

▸Stress-testing a commercial loan against a lender minimum coverage ratio

Benefits

•Shows the maximum amount supported by your own figures
•Identifies which ratio is the binding constraint
•Quantifies how much headroom remains before a threshold
•Lets you compare a stretch scenario with a comfortable one

Limitations

•Lenders apply overlays, compensating factors and their own credit-tier pricing
•Student-loan payments, leased vehicles and child support are counted differently by different programmes
•Self-employed income is usually assessed on tax returns rather than gross revenue
•A ratio that passes on paper can still fail on credit history, reserves or documentation

Best Practices

•Use gross income for debt ratios and net income for your own budget
•Pay down revolving balances rather than shuffling debt between cards
•Keep the requested amount at the comfortable ratio, not the maximum
•Re-run the numbers after any rate change — the same payment supports a smaller loan as rates rise

Common Misconceptions

Myth: A pre-approval guarantees funding

Truth: Pre-approvals are conditional on documentation, appraisal and final underwriting.

Myth: A high income always qualifies

Truth: Existing obligations, credit history and collateral matter as much as income.

Practical Tips

•Set the payment budget from your actual monthly surplus, not a lender’s ceiling.
•Include realistic tax and insurance figures for the ZIP code, not national defaults.
•Check the result at a rate 0.5 points higher — that is your stress test.

Common Mistakes

Buying at the qualification ceiling

The ceiling ignores childcare, commuting and savings; leave visible headroom.

Forgetting closing costs in the cash plan

The down payment is only part of cash to close; add 2%–5% for costs and prepaids.

Assumptions

This calculator makes the following assumptions to provide estimates:

Figures as entered: The result follows directly from the values supplied; lender rounding may differ slightly.

Rate and term fixed: Escrowed costs reassess annually and are modelled as entered.

Limitations

Be aware of these limitations when using this calculator:

Limitation: Lenders apply overlays, compensating factors and their own credit-tier pricing

Limitation: Student-loan payments, leased vehicles and child support are counted differently by different programmes

Limitation: Self-employed income is usually assessed on tax returns rather than gross revenue

Limitation: A ratio that passes on paper can still fail on credit history, reserves or documentation

Frequently Asked Questions

Answers to common questions about this calculator.

Why does the affordable price fall when rates rise?

The same payment services a smaller loan at a higher rate; historically each 1-point rate rise cuts buying power roughly 10%.

Should I use gross or net income for the budget?

Lenders qualify on gross, but households spend net — set the budget from your net cash flow for a sustainable answer.

Who uses the mortgage affordability calculator?

It is used by home buyers comparing mortgage offers, by owners weighing a refinance or equity move, and by loan officers and advisers sanity-checking a payment, ratio or fee structure. It sits in the Mortgage Basics group of the Mortgage & Home Finance section of Atlascalcs.

How accurate is the mortgage affordability calculator?

Every figure follows directly from the inputs using standard amortisation mathematics, so it is accurate to the quality of the values you enter. Lenders round payments and apply their own day-count conventions, so expect small differences against a formal statement or payoff quote.

How current are the rates and thresholds used here?

The calculator uses the figures you enter, so update the rate to your actual offer or current market quote. Ratio thresholds, poverty guidelines and programme rules reflect the conventions described in the references and change periodically.

Does rounding change the results?

Every calculation runs on full precision and rounds only for display. Lenders round payments to the nearest cent or dollar, so expect a small difference between these figures and a formal statement or payoff quote.

Should I use the payment or the total cost to compare offers?

Use the payment to judge cash flow and the finance charge or APR to judge cost. When two offers differ on both, the all-in cost over the period you expect to hold the loan is the decisive measure.

Can I use this calculator for a business or commercial loan?

Yes. The payment, amortisation, ratio and cost calculators apply the same amortisation mathematics to commercial loans; the difference is in the fees, covenants and collateral rules, which you should enter explicitly.

What information should I have ready before applying?

Your exact rate and term, the fee schedule, any required add-ons, and your gross income and existing monthly obligations. With those five numbers every figure on this page can be tied back to a lender quote.

Related Calculators

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Related Guides

Deepen your understanding with these educational resources.

Loan repayment and amortisation guide

How payments split between interest and principal, and how to read a schedule.

Borrowing cost and APR explained

Rate versus APR, points, fees and the cost of a longer term.

Qualifying for credit

The ratios lenders use, and how to improve each one before applying.

Glossary

Technical terms used in mortgage calculations explained in plain language.

Principal: The amount borrowed, excluding interest and fees. Payments applied to principal reduce the balance and therefore future interest.
Amortisation: Repaying a debt through a schedule of payments that gradually shifts the split from interest to principal until the balance reaches zero.
APR (Annual Percentage Rate): The yearly cost of credit expressed as a rate, including interest and most upfront finance charges.
Escrow: An account the servicer holds to pay property taxes and insurance on your behalf, funded monthly as part of the payment.
PITI: Principal, interest, property taxes and insurance — the four components of a full monthly housing payment, sometimes plus HOA dues.
PMI (Private Mortgage Insurance): Insurance protecting the lender when the down payment is below 20% of price; paid by the borrower and removable once equity is sufficient.
Cash to close: The total funds a buyer brings to settlement: down payment plus closing costs plus prepaids, minus credits.

Authoritative References

Trusted sources and standards referenced by this calculator.

Consumer Financial Protection Bureau — Loan options and disclosures Consumer Financial Protection Bureau — What is a debt-to-income ratio? Federal Reserve — Consumer credit (G.19) statistical release Federal Reserve — Consumer credit and leasing guides U.S. Small Business Administration — Loan programmes Federal Student Aid — Income-driven repayment plans Federal Student Aid — Public Service Loan Forgiveness Federal Trade Commission — Consumer credit guidance

Applicable Standards

Level-payment (simple-interest) amortisation, payments assumed in arrearsAPR computed by discounting the actual payment stream to net proceedsDebt ratios computed on gross income for lender comparisonsMoney rounded for display only; all calculations run at full precision

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Page Information

Last Updated:

2026-09-21

Version:

2.0.0

References:

License:

Free to use for educational and professional purposes.