The 30% Housing Cost Rule
Your mortgage should not exceed 30% of net take-home — the leverage safety boundary
When a lender approves you for a mortgage, they are answering one question: can you technically service this debt? They are not answering: will this mortgage leave you with a viable life? Eddie Ross proposes 30% of net take-home pay as the guideline threshold for total housing cost — mortgage payment, not rent, against the bank account figure after tax and national insurance.
The 30% rule creates a buffer for the non-mortgage costs of homeownership: council tax, utility bills, maintenance, insurance, service charges on leasehold properties. These are absent from renting and often underestimated in first-time buyer planning. Beyond 40%, Ross argues the financial logic starts to break down: the buyer is exposed to job loss, rate changes, or family changes without meaningful resilience.
The rule is explicitly lifestyle-dependent. A person with no dependents, low social spending, and strong job security might stretch to 40%. A family with children, a car payment, and school costs should target below 30%. The diagnostic question is whether the housing cost leaves enough disposable income to absorb the what-if scenarios — a change in mortgage rate at remortgage being the most significant.
- Net take-home, not gross salary, is the correct denominator — the government takes its share before you decide on housing.
- 30% creates buffer for rate changes, maintenance costs, and income shocks — above 40% the buffer effectively disappears.
- The right percentage is inversely related to financial dependents: fewer dependents, more flexibility; more dependents, tighter ceiling.
- Lifestyle priorities legitimately shift the threshold — someone who rarely leaves home may rationally pay 40%; a heavy traveller should target 25%.
- Lender approval is a legal ceiling, not a recommendation — approved does not mean sustainable.
- Calculate your net monthly take-homeUse your actual bank deposit after tax, national insurance, pension contributions, and any salary deductions — not your gross salary. For variable income, use a 12-month average.WarningLenders assess gross income but your experience of the mortgage is against net cash — always model on net.
- Set your 30% and 40% thresholdsCalculate 30% and 40% of your net monthly take-home. The mortgage payment should fall between these bounds for most circumstances. If your target mortgage payment exceeds 40%, the property is likely beyond your sustainable affordability even if a lender approves it.Pro tipInclude council tax, building insurance, and an estimated maintenance reserve (1% of property value annually is a common rule of thumb) in your housing cost total, not just the mortgage payment.
- Stress-test the payment at remortgageIf your current mortgage rate is 4%, recalculate what the monthly payment would be at 7% (a plausible spike at remortgage). Confirm the stressed payment still falls below 40% of net income. If it does not, you are taking on rate-risk exposure.WarningThe period of maximum risk is remortgage — you cannot control rates at that moment, so your budget needs to absorb an upside scenario.
- Adjust for life stage and dependentsIf you have or plan to have children within the mortgage term, model what childcare costs (£800–2,000/month in many UK cities) do to your disposable income. A 30% mortgage that works today may become a 50% effective burden after childcare is accounted for.Pro tipCouples buying together should model both single-income scenarios — what happens if one partner stops working due to a child, illness, or redundancy?
Ross is paying 40% of his net take-home on rent in London. He is explicit that this is tolerable only because he has no children. He frames 40% as the ceiling, not the target, and uses himself as a real case study in why the rule is lifestyle-conditional.
A listener asked what ratio of take-home should go to mortgage. Ross gave the 30% number with the direct caveat that without dependents, 40% is justifiable — but at 50% you start questioning whether you should own the house at all.
Ross arrived at this heuristic from both the lender underwriting framework (where 30% approximates the affordability boundary many lenders use in their budget plans) and from observing customers whose mortgage payments exceeded 40–50% of take-home. He uses his own situation as a data point: his rent at 40% of take-home is manageable without dependents but he is explicit it would not be if he had children.