How much of your income should you spend on a mortgage?

When most people ask, “What percentage of income should go toward a mortgage?” what they’re really asking is: What’s safe, what’s normal, and what will let me live my life without financial strain?

It’s a fair question. Buying a home is often the single largest financial commitment a person or household will make. But while banks will gladly approve you for the highest amount your income can carry, that doesn’t mean it’s the right fit for your long-term plans.

There’s no one-size-fits-all number. But there are planning frameworks that can help you move beyond the default—and toward a decision that reflects both your life stage and future goals.

You’ve probably heard of the 30% rule: spend no more than 30% of your gross monthly income on housing. It’s widely repeated because it feels easy to remember, and it aligns with many affordability benchmarks used by mortgage lenders and housing policy guidelines. This rule originated in the mid-20th century, based on US federal housing policy, and has since become a catch-all reference point. But there’s one big problem with it: it assumes a household with no major debt, stable employment, and average costs for everything else.

In practice, that’s rare. Today’s homebuyers are balancing student loans, higher childcare costs, dual-income volatility, and rising food and energy bills. So while the 30% rule is a reasonable baseline, it often needs adjustment based on real-world complexity.

To dig deeper, let’s look at how mortgage lenders actually assess affordability.

Front-End Ratio: This refers to the percentage of your gross monthly income that goes toward housing costs—typically including mortgage principal, interest, property tax, and insurance (PITI). The industry norm is to keep this under 28% to 31%.

Back-End Ratio: This adds in your other monthly debt obligations—like student loans, car payments, and credit card minimums. Lenders typically want this below 43%, though some stretch to 50% with strong credit.

Here’s the catch: just because you can qualify with ratios up to 43% or 50% doesn’t mean you should borrow that much. The gap between qualification and comfort is where financial clarity lives.

Instead of chasing a fixed number, try viewing mortgage affordability as a zone system:

Zone 1 – Conservative (20–25% of gross income)
Ideal for: First-time buyers, single-income households, or those in uncertain industries.
This zone leaves room for aggressive saving, lifestyle flexibility, and futureproofing against job changes or rising costs. The trade-off may be a smaller property or longer commute—but financial breathing room is maximized.

Zone 2 – Balanced (25–30% of gross income)
Ideal for: Dual-income families with stable employment and moderate fixed expenses.
This is the sweet spot for many professionals. It allows room for investment goals, holidays, and education planning without overleveraging your income. Cash flow remains manageable, even if one income is temporarily reduced.

Zone 3 – Stretched (30–40%+ of gross income)
Possible for: Buyers in high-cost urban areas or those prioritizing location and space over liquidity.
If your back-end ratio remains under control, some lenders may still approve this. But the margin for error narrows. Lifestyle trade-offs often follow: fewer savings, delayed retirement contributions, or higher stress if unexpected expenses arise.

Ask yourself: which zone fits not just your finances, but your life priorities?

While most lender formulas use gross income (your income before taxes and deductions), it’s worth planning based on your net income—what actually hits your bank account. A mortgage that takes up 30% of your gross income might eat up 40% or more of your take-home pay, especially in higher-tax jurisdictions. This is where people often feel house-poor: technically “affording” the loan, but struggling to save or enjoy daily life.

To avoid this trap, recalculate your target percentage using your net income. For example:

• Gross income: $6,000/month
• Net income after taxes/CPF/etc.: $4,500/month
• 30% of gross = $1,800/month (standard rule)
• 30% of net = $1,350/month (a more sustainable lens)

That $450/month difference may represent the gap between progress and pressure.

Your repayment structure matters just as much as the percentage you spend. A variable-rate mortgage that starts affordable may quickly become unsustainable in a rising interest rate environment. This is particularly relevant in markets like Singapore or Hong Kong, where floating-rate packages are common. A buyer may start with a low teaser rate and comfortably fit within the 30% target—only to find repayments rising dramatically after the first year.

One rule of thumb: only treat a mortgage as “affordable” if it still fits within your chosen zone after simulating a 2–3 percentage point rate hike. If you're considering a floating-rate mortgage, run the numbers for worst-case repayments—not just the starting deal.

In cities like Singapore, London, or San Francisco, the 30% rule often breaks down. Housing costs frequently exceed that threshold, especially for buyers without intergenerational wealth. So what do you do when even modest homes push you into the “stretched” zone?

Start by rethinking your timeline. Are you buying for the next 5 years—or the next 30? A higher short-term ratio might be acceptable if you expect income growth or plan to refinance. But if your career stage is plateauing, or you’re adding dependents, the cushion matters more. You can also explore a different frame: instead of asking “How much mortgage can I carry?” ask “How much home equity can I reasonably build over time?” The goal isn’t to max out your borrowing—it’s to own with confidence and control.

A house isn’t just a place to live—it’s one part of a broader financial plan. That’s why your mortgage budget must work in harmony with other priorities, like:

• Emergency savings (ideally 3–6 months of living expenses)
• Retirement contributions (CPF, SRS, or private investing)
• Children’s education savings
• Insurance protection (life, disability, health)
• Lifestyle resilience (travel, caregiving, flexibility)

If your mortgage prevents you from making progress on all of the above, it’s too big—no matter what the bank says. Housing shouldn’t come at the cost of total financial health.

In Singapore, many homeowners use CPF Ordinary Account (OA) savings to pay their mortgage. This can make repayments feel more affordable, since they don’t reduce monthly cash flow. But there are trade-offs. Using too much CPF can erode your retirement savings and affect CPF interest compounding. It may also reduce the resale value you can retain in cash, due to accrued interest obligations.

Ask yourself:

• Can you cover part of the mortgage in cash, to preserve CPF for retirement?
• Have you accounted for the refund you’ll owe to CPF if you sell?
• Does your current CPF use match your future housing and retirement plans?

CPF is a helpful tool—but it’s not “free money.” Using it well means knowing what you’re trading.

Finally, your mortgage comfort zone depends on your income volatility and household setup. A few examples:

• Single-income families: Should stress-test the mortgage against one partner’s income. If one stops working, does the loan still fit?
• Freelancers or commission-based earners: Should use average monthly income over 12–24 months, and set a lower baseline to allow for dry spells.
• Early-career professionals: Can start smaller and “ladder up” over time—but only if job stability and income growth are likely.

You don’t just need a mortgage you can pay. You need one you’ll still want to pay in three, five, or ten years—without sacrificing the rest of your life.

A mortgage isn’t just a transaction. It’s a long-term relationship with your income, your housing market, and your life decisions. That’s why asking “what percentage of income should go toward a mortgage?” is only the first step.

A better question is: What housing cost lets me live the life I actually want—today, and in the future? Don’t aim for the maximum. Aim for what gives you freedom to pivot, save, rest, and build. That’s what makes homeownership truly sustainable. And that’s what turns a loan into a foundation for financial clarity.