How Much House Can I Afford? A Complete Calculation Guide

The question "how much house can I afford?" has two different answers: what a lender will approve, and what you can genuinely afford without compromising other financial goals. The lender's number is the ceiling. Your real number should be lower.

How Lenders Calculate Your Maximum Loan

The Debt-to-Income Ratio (DTI)

The DTI ratio is the central criterion most lenders use. It compares your total monthly debt obligations to your gross monthly income.

In the US, conventional lenders typically require a back-end DTI (all debts including the mortgage) below 43–45%. In the UK, lenders use income multiples (typically 4–4.5x annual salary) more commonly than explicit DTI ratios, though both approaches yield similar results.

Front-End vs Back-End DTI

• Front-end DTI: Housing costs only (mortgage P&I, taxes, insurance) / gross income. Target: below 28%.
• Back-end DTI: All monthly debt payments (housing + car loans + student loans + credit cards) / gross income. Target: below 43%.

Example Calculation

Gross monthly income: €5,000. Existing monthly debts (car loan, student loan): €400.

• Maximum back-end DTI at 43%: €5,000 × 43% = €2,150 total monthly obligations
• Maximum housing cost: €2,150 − €400 = €1,750/month
• At 4.5% interest over 25 years, €1,750/month services approximately a €310,000 mortgage
• With a 20% deposit, maximum property price = €310,000 / 0.8 = €387,500

The Hidden Costs That Reduce What You Can Afford

Monthly mortgage payment is only part of the housing cost. The realistic total includes:

• Property taxes / ground rent: 0.5–2% of property value per year, depending on location
• Buildings insurance: €150–€500/year
• Service charges (flats): Can be €1,000–€5,000/year for managed blocks
• Maintenance: Budget 1% of property value per year
• Utilities: Often higher in a larger or older property

A conservative rule: total housing costs (including all the above) should not exceed 30–35% of gross income.

Why Lender Maximum ≠ Your Maximum

Lenders approve loans up to what they calculate you can service. They don't account for:

• Your retirement savings goals
• Emergency fund maintenance
• Children's education costs
• Career risk (what if you lose your job?)
• Lifestyle costs that aren't captured in credit reports
• Future rate increases if you're taking a variable rate or short-term fixed

A borrower approved for €400,000 who stretches to buy a €400,000 property has no margin for error. Aim to borrow 10–20% less than your approved maximum — the payment difference is small, but the financial breathing room is significant.

How Interest Rates Change Affordability

A 1% rise in mortgage rates reduces your purchasing power by approximately 8–10%. This is why affordability tightened so dramatically when rates rose from 1% to 5% in 2022–2023: buyers who could afford a €350,000 home in 2021 could suddenly only afford €250,000–€280,000 on the same income.

25-year term. Monthly payments include principal and interest only. All figures are approximate.

The Deposit: How Much is Enough?

A larger deposit reduces your mortgage, your monthly payment, and your LTV ratio — which usually unlocks better interest rates. Key thresholds:

• 5% deposit: Possible in many markets, but requires mortgage insurance or premium rates. High LTV = high risk.
• 10% deposit: Significantly better rates than 5%. More accessible for first-time buyers.
• 20% deposit: Typically avoids mortgage insurance entirely and accesses the best rate tiers.
• 25%+ deposit: Access to lenders' best rates; significantly lower monthly costs.