Maximum Mortgage Calculator

DTI as the Mortgage Ceiling

Debt-to-income ratio is the single most influential affordability number. Lenders commonly cap combined DTI (total debt payments divided by gross income) around 36 to 43 percent. The mortgage payment must fit inside that cap alongside any existing debts. This calculator works backward from that constraint to the maximum loan amount.

Adjusting the DTI Target

Default 36 percent is a conservative target. Some lenders and government-backed loan programs allow higher ratios, often in the 43 to 50 percent range, though the exact limits vary by country and lender. Entering a higher DTI gives a larger maximum loan but tighter monthly cashflow after closing. A lower DTI, such as below 36 percent, leaves a larger monthly buffer for unexpected costs.

Quick example

With gross monthly income of 8,000 and existing monthly debt payments of 600 (plus interest rate of 6.5 and loan term of 30), the result is 360,720.67. Change any figure and watch the output shift — it's often more useful to see the pattern than to memorise the formula.

Which inputs matter most

You enter Gross Monthly Income, Existing Monthly Debt Payments, Interest Rate, Loan Term, and Max DTI Target. Not every input has equal weight. Adjusting one input at a time toward extreme values shows which ones move the result most.

What's happening under the hood

Calculates maximum monthly mortgage payment as (gross monthly income times DTI percent) minus existing debts, then converts to principal via standard amortization formula. Results are estimates for illustration purposes only and do not factor property taxes, insurance, or PMI. The formula is listed in full below. If the number looks off, you can retrace the calculation by hand — that's the point of showing the working.

Why this matters

A mortgage is usually the biggest single financial commitment a person makes. The difference between a well-chosen product and a hasty one can run into tens of thousands over the life of the loan. Modelling the numbers ahead of a decision shows how sensitive the outcome is to the rate and structure chosen.

What this doesn't capture

The figure shown reflects the core calculation; additional costs such as arrangement fees, valuation, legal fees, insurance, and any early-repayment charges (where applicable) sit on top and can add materially to the total cost of borrowing. Rates and product terms can also change over the life of the loan, which can shift the picture relative to this fixed-snapshot estimate.