How Much House Can I Afford? A Clear Guide

The Lender vs Borrower Perspective

When you apply for a mortgage, a bank will run its calculations and tell you the maximum amount it is willing to lend you. That figure is based on your income, your existing debts, your credit history, and the regulatory limits that apply in your country. It is designed to reflect the maximum loan the bank believes you can service — but that is a very different question from what is actually comfortable for you to repay.

The maximum a lender offers is a ceiling, not a target. Lenders are not focused on whether you will be able to contribute to your retirement, build an emergency fund, take a holiday, or handle an unexpected car repair while repaying the mortgage. They are focused on whether you will default. Those two things are not the same.

People who borrow the absolute maximum a lender will offer frequently end up in a situation personal finance advisers call "house poor" — technically solvent, but with so much of their income consumed by housing costs that they have no financial flexibility for anything else. The house owns them rather than the other way around.

A more useful question to ask before you start house hunting is this: what monthly repayment leaves enough room for savings, for emergencies, and for the ordinary costs of life? Start with that number and work backwards to a purchase price — rather than starting with the largest loan the bank will offer and trying to make your budget fit around it.

The 28% Front-End Rule (US)

The most widely cited rule for US homebuyers is that your total monthly housing payment should not exceed 28% of your gross monthly income. Lenders call this the front-end debt-to-income (DTI) ratio. The housing payment they measure is not just principal and interest — it is your full PITI: principal, interest, property taxes, and homeowners insurance combined.

Here is how that plays out with a concrete example. Suppose your gross annual income is $80,000. Your gross monthly income is $6,667. Applying the 28% rule gives you a maximum PITI of $1,867 per month. That is the outer limit according to this guideline — not a number you necessarily want to be at, but the upper boundary of what most advisers consider prudent.

At a 7% mortgage rate over a 30-year term, a monthly payment of $1,867 (before taxes and insurance) supports a loan of roughly $280,000. If you are budgeting $300 per month for taxes and insurance — a conservative estimate in many markets — your principal-and-interest payment would be $1,567, which supports a loan of approximately $235,000. Taxes and insurance are not optional extras; they reduce the loan size your budget can support by a meaningful amount.

The 36% Back-End DTI Rule (US)

The front-end rule looks only at housing costs. The back-end DTI rule looks at your total debt obligations — every monthly payment you make including the mortgage, car loans, student loans, and minimum credit card payments. The traditional guideline is that total debt payments should not exceed 36% of gross monthly income.

It is worth knowing that many lenders today will approve mortgages at back-end DTIs up to 43% — and some government-backed loan programs allow even higher. But 36% is the level where most experienced financial advisers believe you still have genuine breathing room. Above that, you are increasingly dependent on everything going right.

The back-end rule often becomes the binding constraint for buyers who carry existing debt. Continuing the earlier example: gross monthly income of $6,667. At 36%, total debt payments cap at $2,400. If you already pay $500 per month on car loans and student loans, only $1,900 remains for your mortgage. That is a lower ceiling than the front-end rule suggested — and it is the lower number that governs.

Before applying for a mortgage, it is worth making a complete list of every monthly debt payment you carry. Many buyers underestimate this figure because they think only of their biggest debts and forget minimum credit card payments, personal loans, or financing arrangements on appliances or electronics.

Lending Rules by Country

The specific DTI ratios used in the US do not map directly onto other countries, which each have their own regulatory frameworks for mortgage lending. Here is how affordability is assessed in three other major markets:

United Kingdom (GBP):

UK lenders typically cap mortgage offers at 4.5 times your annual income, though some lenders extend to 5 or even 5.5 times for high earners in certain professions. More importantly, lenders are required to stress-test affordability at a rate approximately 3 percentage points above the mortgage rate offered. This means that if you are offered a rate of 4.5%, the lender must confirm you could afford repayments at 7.5%. If you earn £50,000 per year, the maximum loan at 4.5x income is £225,000 — subject to that stress test passing.

Australia (AUD):

The Australian Prudential Regulation Authority (APRA) requires all authorised lenders to stress-test mortgage serviceability at the loan interest rate plus 3 percentage points. A loan offered at 6.5% must be assessed at 9.5%. This is a meaningful hurdle — it means the loan you qualify for is often considerably smaller than the loan you could service at the actual rate. Australian lenders also look at your living expenses in detail, not just your income and existing debts.

Canada (CAD):

Canada uses two ratio tests. The Gross Debt Service (GDS) ratio measures housing costs — mortgage principal and interest, property taxes, and heating costs — as a share of gross income and must remain below 32%. The Total Debt Service (TDS) ratio adds all other debt payments and must remain below 44%. Additionally, Canadian mortgages are stress-tested at the higher of 5.25% or the contracted rate plus 2 percentage points, regardless of the rate you are actually offered. This stress test applies to all insured and most uninsured mortgages.

Across all countries, lenders also weigh factors beyond pure ratios: your credit score and history, the stability of your employment (self-employed borrowers typically face additional scrutiny), the size of your deposit relative to the purchase price, and any existing financial obligations beyond debt — such as child maintenance payments.

The Deposit: Why It Changes Everything

The size of your deposit affects your mortgage in three ways: it determines how much you need to borrow, it influences the interest rate you are offered (smaller deposits typically attract higher rates), and it determines whether you are required to pay mortgage insurance. That third factor is the one most buyers underestimate.

In the United States, buying with less than a 20% deposit typically triggers a requirement to purchase Private Mortgage Insurance (PMI). PMI protects the lender — not you — against the risk of default. The cost is typically 0.5 to 1.5% of the loan amount per year, added to your monthly payment. On a $350,000 loan, that is $1,750 to $5,250 per year — or $146 to $438 per month — for coverage that benefits only your lender. PMI falls away once you have built 20% equity in the property.

In the United Kingdom, there is no legal equivalent to PMI, but lenders restrict their best rates to borrowers with deposits of 20% or more. A buyer with a 10% deposit will typically pay a meaningfully higher interest rate than one with a 25% deposit, which compounds over the life of the mortgage into a substantial additional cost.

In Australia, any buyer with less than a 20% deposit is required to pay Lenders Mortgage Insurance (LMI). Unlike PMI, LMI is typically charged as a single upfront premium rather than a monthly addition — and it can be significant. Depending on the loan size and deposit percentage, LMI can cost anywhere from $5,000 to $20,000 or more. Most lenders allow this to be added to the loan, but doing so means paying interest on it for the life of the mortgage.

In Canada, any mortgage with a deposit below 20% is classified as a high-ratio mortgage and must be insured through the Canada Mortgage and Housing Corporation (CMHC) or a private equivalent. The insurance premium ranges from 2.8% to 4.0% of the loan amount depending on the deposit size, and it is added to the mortgage principal. On a $500,000 loan with a 10% deposit, the CMHC premium at 3.1% adds $13,950 to the amount borrowed — which then accrues interest over the full amortisation period.

Hidden Costs to Budget For

Your deposit and your mortgage repayments are not the only costs involved in buying a home. First-time buyers frequently underestimate the additional cash required to complete a purchase, which can cause serious stress if those funds are not available when needed. Budget carefully for the following:

• Stamp duty / property transfer tax: In the UK, Australia, and Canada, the government charges a tax on property purchases that can amount to tens of thousands of dollars or pounds depending on the purchase price and jurisdiction. Use a Stamp Duty calculator to get a precise figure for your situation before you make an offer.
• Legal and conveyancing fees: You will need a solicitor or conveyancer to handle the legal transfer of ownership. Expect to pay £1,000–£3,000 in the UK, $1,500–$3,000 in Australia, and $1,000–$2,000 in Canada. US closing costs, which include legal fees, title insurance, and lender fees, typically range from 2–5% of the loan amount.
• Building survey or home inspection: A professional inspection of the property before purchase is essential and can prevent costly surprises. Budget $300–$800 depending on property size and location.
• Moving costs: Professional removals or truck hire, packing materials, and any storage needed typically cost $1,000–$5,000 depending on the distance and volume of possessions.
• Initial repairs and furnishings: Very few homes are move-in ready without some spending on repairs, redecoration, or new furniture. This category is consistently underestimated by first-time buyers, particularly when purchasing older properties.

A Worked Example

To see how these rules interact in practice, consider the following profile: a US couple with a combined gross income of $120,000 per year. They carry a $400 per month car payment. They also have student debt with $10,000 remaining, but it will be fully paid off in two years.

The monthly payment breaks down to approximately $2,530 in principal and interest, plus around $270 per month in property taxes and homeowners insurance — totalling $2,800, exactly at the 28% front-end limit. There is no PMI because the deposit is 20%. This is a workable budget, but it is at the edge of what the guidelines suggest — the couple would be wise to aim for a purchase price $30,000–$50,000 below this ceiling to give themselves a genuine financial buffer.