1. The 28/36 rule (or DTI guideline)
Lenders look at two ratios:
- Front-end ratio: your housing payment (principal, interest, tax, insurance) should be under 28% of gross monthly income.
- Back-end ratio (DTI): all debt payments combined — including housing — should be under 36% of gross monthly income.
These are guidelines, not rules. Some lenders allow up to 43% DTI; others stay below 36%. This calculator uses a conservative 36% DTI as a starting point, and adjusts by country.
💡 Just because a lender approves a certain amount doesn't mean you should borrow it. Use this calculator to find a comfortable number, not just a maximum.
2. Working backwards from your budget
We start with your monthly income, subtract your existing monthly debts, and apply the DTI ratio to get a maximum monthly housing budget. From that, we subtract estimated property tax, home insurance, and HOA fees. What's left is the maximum monthly principal & interest payment — which we convert into a loan amount using the standard mortgage formula.
Max housing budget = (Gross monthly income × DTI) − Existing monthly debts
Max P&I payment = Max housing budget − (Tax + Insurance + HOA)
Max loan amount = P&I × [(1+r)ⁿ − 1] ÷ [r × (1+r)ⁿ]
3. Adding your down payment
The final step is simple: your affordable home price is the maximum loan amount plus your down payment.
✓ Your affordable home price = Maximum loan amount + Your down payment
4. What this doesn't include
- Closing costs: budget 2%–5% of the home price for legal fees, registration, stamp duty, and lender fees.
- Moving and setup costs: often overlooked — can add thousands.
- Maintenance: budget 1% of home value per year for repairs and upkeep.
- Emergency reserves: keep 3–6 months of expenses in cash after closing.
- PMI or LMI: if your down payment is below 20% in the US, Canada, or Australia.
5. How the ratios vary by country
- US: 28/36 rule. Lenders may allow up to 43% DTI; below 36% is safest.
- UK: Lenders typically cap at 4–4.5× income, plus affordability stress tests.
- Canada: Gross Debt Service (GDS) under 32%, Total Debt Service (TDS) under 40%.
- Australia: Lenders look at a 30%–35% total debt ratio, plus a buffer on interest rates.
- India: FOIR of 40%–55% depending on income and employment type.
6. Where people go wrong
- Borrowing the maximum. Approvals don't leave room for surprises.
- Ignoring property tax. It varies hugely by location — and can add hundreds to your monthly payment.
- Forgetting maintenance. A home costs far more than just the mortgage.
- Not budgeting for closing costs. 2%–5% of the price, paid upfront.
- Stretching income assumptions. Use stable, verifiable income — not your best-case bonus.
7. Final thoughts
Affordability is personal. The math gives you a range; only you can decide what feels comfortable. A slightly smaller home or a slightly longer savings runway can mean decades of financial breathing room.
Use this calculator as a starting point. Then talk to a lender, verify the numbers, and — most importantly — leave yourself a buffer.