Loan Affordability Calculator
A loan affordability calculator works backwards from a payment calculator. Instead of asking "what is the payment on this loan", it asks "how big a loan can my income actually carry". You give it your income, your existing debt payments, and the debt-to-income (DTI) limit you or your lender wants to respect, and it returns a concrete borrowing ceiling — the largest loan whose payment still fits inside your budget.
- Max monthly payment (new loan)
- $1,300.00
- Max loan amount
- $183,932.97
- DTI used
- 36.00%
- Total interest over term
- $206,067.03
DTI (debt-to-income) is the share of your gross monthly income that goes to debt payments. At a 36% cap on 5,000 of income, lenders allow about 1,800 toward all debt; after your existing 500, roughly 1,300 is free for a new loan payment. That is a ceiling, not an approval — lenders also weigh your credit score, down payment, employment history, and the property itself.
How it works
The calculation runs in two steps. First it sizes your monthly headroom: it takes your gross income, multiplies by the DTI cap to get the total a lender will let you spend on all debt, then subtracts the debt payments you already have. What is left is the most you can put toward a new loan each month.
Second, it converts that payment into a principal. A given monthly payment supports a smaller loan at a higher rate or a shorter term, and a larger loan at a lower rate or a longer term. The calculator inverts the standard amortization formula to find the exact principal that produces a payment equal to your headroom — that is your ceiling.
DTI is the lever most people overlook. Lenders commonly look at two versions: a front-end ratio covering just housing, and a back-end ratio covering all debt, often capped around 36% to 43%. Existing obligations like a car loan or credit-card minimums eat into the same budget, so paying them down can raise your ceiling more than a small rate improvement would.
Max payment = (income × DTI%) − existing debts. Max loan = PMT · ((1 + i)^n − 1) / (i · (1 + i)^n), where PMT = max payment, i = annual rate ÷ 12 ÷ 100, and n = years × 12. This is the inverse of the EMI formula: it solves for the principal a payment can support rather than the payment a principal requires.
Worked example
Suppose you earn 5,000 a month gross, already pay 500 toward existing debts, and apply a 36% DTI cap. Your total debt budget is 5,000 × 36% = 1,800. Subtract the 500 you already owe and 1,300 a month is free for a new loan. At 7% over 25 years (300 months), 1,300 a month supports a loan of roughly 184,000. Over the full term that loan costs about 206,000 in interest. Trim the existing debts to 200 and the free payment jumps to 1,600, lifting the ceiling to around 226,000.
Things to watch out for
If your existing debt payments already meet or exceed your DTI budget, there is no room for a new loan and the calculator says so rather than returning a negative number — the fix is to reduce existing debt or raise the cap. Note the figure is a ceiling, not a recommendation: borrowing right up to your DTI limit leaves no margin for emergencies, so many borrowers deliberately aim well below it. Lenders also apply their own underwriting on credit, down payment, and income stability, so an approval may come in lower than this number.
Frequently asked questions
What is a debt-to-income (DTI) ratio?+
It is the share of your gross monthly income that goes to debt payments. Lenders use it to gauge how much more debt you can safely take on; a common back-end cap is around 36% to 43% of income across all debts.
Should I borrow the maximum this shows?+
Not necessarily. The result is the ceiling your DTI allows, not a comfortable target. Borrowing the full amount leaves no buffer for rate changes, emergencies, or new expenses, so many people choose to stay well under the limit.
Why do my existing debts lower the amount so much?+
Existing payments come out of the same DTI budget as the new loan. Every unit of existing debt payment is a unit less available for the new loan, and because that payment is leveraged across years, a small reduction can raise your ceiling significantly.
Will a lender actually approve this amount?+
Maybe, but DTI is only one factor. Lenders also weigh your credit score, down payment, employment history, and the asset itself. Treat this as a planning ceiling and confirm the real figure with a pre-approval.
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Disclaimer: This calculator is for educational and informational purposes only and provides estimates, not financial advice. Interest rates, taxes, fees, and local rules vary and change over time. Confirm figures with a qualified professional before making any financial decision.
Last reviewed: 2026-06-22