Mortgage Affordability Calculator

What this calculator is, and when to reach for it

There are two very different questions hiding inside "how much house can I afford", and confusing them is how people end up house-poor. The first is what a lender will hand you. The second is what you can carry without your life narrowing around the payment. This calculator answers the first one honestly, and gives you the levers to answer the second one for yourself.

Lenders decide by looking at how much of your income is already spoken for. They apply two ceilings. The housing ratio, sometimes called the front-end ratio, caps what your housing payment alone may be as a share of your gross income. The total-debt ratio, or back-end ratio, caps everything together: the new housing payment plus your car finance, student loans, card minimums, and any other monthly obligation. You enter both percentages, because they are conventions rather than laws, and they vary by lender, by loan programme, and by country.

The calculator works out both ceilings, takes whichever one binds, subtracts the ownership costs you entered, and turns the payment that is left into a loan amount using your rate and term. Then it tells you which ceiling was the one that actually held you back, which is the single most useful output on the page. If the housing ratio binds, your income is the constraint. If the total-debt ratio binds, your existing debts are the constraint, and clearing one of them may do more for your budget than earning more.

One thing to be deliberate about: enter your income before tax and deductions, because that is the figure lenders assess against. It is not the money that lands in your account. This is precisely why a number that clears every lender ratio can still feel unaffordable in practice, and why the result here is a ceiling rather than a recommendation.

Reading the answer like a lender would

The figure this page produces is an estimated loan amount, not a house price. The price you could consider is the loan plus whatever deposit you bring, which is why two people on identical incomes shop in completely different brackets. To go from a loan to a price, carry the number across to the home affordability calculator.

Treat the result as the top of a range, never a target. Lenders assess more than ratios: credit history, how long you have been earning, how stable that income looks, the property itself, and their own appetite that month. Two lenders given the same file routinely return different answers.

The optional cost fields matter more than they look. Property tax, insurance, and service charges are usually collected inside your monthly payment, so every unit you enter comes straight off the payment available for principal and interest, which then shrinks the loan you qualify for. Leaving them blank does not make the costs disappear. It just moves the surprise to later.

Where to go next

Once you have a ceiling, pressure-test it. Take the loan figure to the mortgage calculator to see the actual monthly payment, and to the amortization calculator to see what that commitment looks like across thirty years rather than one month.

If the total-debt ratio was the binding constraint, the debt-to-income calculator shows exactly where your income is already committed, and the credit card payoff and debt consolidation calculators show what clearing a balance would free up.

On the deposit side, the down payment calculator and the loan to value calculator show how much cash changes both the loan and whether mortgage insurance applies. For a formal view of the same ground, the mortgage qualification calculator frames it as a lender would, and the buying a home journey walks the whole sequence in order.

How the affordable amount is worked out

The calculation runs in four steps, and you can follow every one of them by hand.

housing cap = I × h   |   debt cap = (I × t) − d   |   P&I = min(caps) − c

I

gross monthly income, before tax and deductions

h

the housing ratio you entered, as a decimal

t

the total-debt ratio you entered, as a decimal

d

your existing monthly debt payments

c

monthly ownership costs: tax, insurance, and service charges

Step one: get to a monthly income

If you enter an annual figure, it is divided by twelve. Everything downstream is monthly, because that is the rhythm a lender assesses and the rhythm you actually live in.

Step two: work out both ceilings

The housing ceiling is simply income multiplied by your housing ratio. The total-debt ceiling is income multiplied by your total-debt ratio, then reduced by everything you already pay each month. That subtraction is the whole reason existing debt shrinks what you can borrow: every unit committed elsewhere is a unit that cannot go toward a mortgage.

Step three: take the lower one, then remove ownership costs

The smaller ceiling is the one that binds, because a lender needs both satisfied. From it, the calculator subtracts the monthly property tax, insurance, and association charges you entered, since those are collected alongside the loan. What remains is the money genuinely available for principal and interest.

Step four: turn a payment back into a loan

The final step runs the amortization formula in reverse: given a payment, a rate, and a term, what balance would produce exactly that payment? This is why the rate matters so much here. The same payment supports a much larger loan at 4% than at 8%, which is how affordability can shift by six figures without your salary changing at all.

It also means a longer term appears to increase what you can afford, because it lowers the payment. It does not increase what the house costs you. The mortgage calculator shows the interest that trade quietly adds.

Why ratios, and why these ones

Ratio limits exist because payment shock, not income, is what causes most defaults. Capping the share of income committed to debt leaves room for the things a lender cannot see: maintenance, a broken boiler, a lean month.

The commonly cited pairing is 28% for housing and 36% for total debt, which is where the conventional guidance sits. Government-backed and specialist programmes often allow considerably more, and some lenders will stretch further with strong compensating factors such as a large deposit or substantial savings. Because the acceptable figures vary so widely, this calculator asks you to choose rather than baking in an assumption you cannot see.

What the ceiling still leaves out

Ratios ignore almost everything about your actual life. Childcare, commuting, medical costs, how many people depend on the income, and whether that income is steady or lumpy are all invisible to the calculation. So is the money a home quietly demands after you own it: maintenance, repairs, and the furniture for rooms you did not previously have.

A useful discipline is to run the number the calculator gives you, then run it again at a payment you would be comfortable with in a bad month, and treat the gap between them as your real margin of safety.

What this page assumes

The calculator works out a housing payment limit and a total-debt payment limit from the percentages you enter, takes off any ownership costs you entered, and estimates the loan from what is left.

It does not apply lender, credit-score, employment, country, or government-program rules.

Worked examples, step by step

Take someone earning 96,000 a year before tax, paying 450 a month on existing debts, using the conventional 28% and 36% ratios, at a 6.5% rate over 360 months. Monthly income is 8,000.

Which ceiling binds

Here the housing ratio binds, at 2,240 against 2,430. That is genuinely good news: existing debt is not what is holding this borrower back, so clearing the 450 would barely move the answer. Income is the constraint. Notice how close the two ceilings are, though. Another 200 a month of debt would flip which one binds, and from that point every extra unit of debt would come straight off the loan.

Now add the costs that actually get collected

Suppose property tax runs 450 a month and insurance 130. Those 580 come out of the binding ceiling before any loan is worked out, leaving 1,660 for principal and interest. The estimated loan falls to 262,630.

That is a drop of over 91,000 in borrowing power from two costs many people leave blank on a first pass. They were always going to be paid. The only question was whether the estimate admitted it.

The same borrower, with and without ownership costs

Two lessons fall out of this. First, always fill in the optional cost fields before you trust an affordability number, because they move it more than almost anything else. Second, watch which ceiling binds. It tells you whether your next move should be earning more, borrowing at a better rate, or clearing a debt.

The vocabulary, on and around this page

Affordability

An estimate of the largest loan your income and existing commitments could support under the ratio limits you choose. It is a ceiling, not a recommendation or an offer.

Gross income

Income before tax and deductions. Lenders assess against this figure, which is why an affordable-looking result can still feel tight against take-home pay.

Housing ratio

The share of gross income a lender will allow for the housing payment alone, also called the front-end ratio. A commonly cited figure is 28%.

Total-debt ratio

The share of gross income allowed for all monthly debt payments including the new housing payment, also called the back-end ratio. A commonly cited figure is 36%.

Binding constraint

Whichever of the two ratio ceilings comes out lower and therefore sets the answer. It tells you whether income or existing debt is limiting you.

Existing monthly debt

The recurring payments you already owe, such as car finance, student loans, and card minimums. These reduce the total-debt ceiling directly.

Principal and interest

The part of a housing payment that repays the loan itself. Ownership costs are collected alongside it but are not part of the loan.

Escrow costs

Property tax, insurance, and similar bills collected inside the monthly payment. Every unit of these reduces the payment available for principal and interest.

Association charges

Recurring dues for a managed building or development, sometimes called service charges or HOA fees. Lenders count them as part of the housing payment.

Loan programme

A specific lending product with its own ratio limits, deposit rules, and insurance requirements. Programmes differ widely by country and by lender.

Compensating factors

Strengths such as a large deposit, substantial savings, or a long stable earning history that can persuade a lender to allow ratios above its usual limits.

Pre-qualification

An informal estimate of what a lender might offer, based on figures you supply without verification. It is not a commitment to lend.

Pre-approval

A more formal review in which a lender verifies income, debts, and credit before indicating an amount. Stronger than pre-qualification but still not final.

Down payment

The cash you contribute up front. Affordability estimates a loan, so the price you could consider is that loan plus your deposit.

Loan to value

The loan as a percentage of the property value. It affects the rate offered and whether mortgage insurance is required.

Mortgage insurance

A premium often required when the deposit is small. It adds to the monthly housing cost and therefore reduces what you can borrow.

Payment shock

A large jump between what you pay for housing now and what you would pay after buying. Lenders watch it because it predicts difficulty better than income alone.

Term

How long the loan runs. A longer term lowers the payment and so raises the affordable loan, without making the property any cheaper overall.

Residual income

What is left after all debts and living costs are paid. Some lending programmes test it directly because ratios alone ignore household circumstances.

Underwriting

The lender’s full assessment of credit, income, employment, and the property before a final decision. Ratios are only one input to it.

Common mistakes, and what this page will not do

• Entering take-home pay instead of gross income. Ratios are assessed against income before tax. Using net pay understates the ceiling badly, often by a third or more.
• Leaving the ownership cost fields blank. Tax, insurance, and service charges are collected with the payment. Omitting them can overstate borrowing power by tens of thousands, as the worked example shows.
• Treating the ceiling as a target. The result is the most a set of ratios would allow, not the amount you should borrow. Comfort lives somewhere below it.
• Forgetting a debt that is about to start. A car loan you are about to sign or a payment resuming after a pause still counts. Lenders look at commitments, not just current statements.
• Assuming 28 and 36 are rules. They are conventions. Programmes and lenders vary widely, and some allow far more with compensating factors. Enter the figures that match your situation.
• Ignoring which ceiling binds. If the total-debt ratio binds, clearing a balance may raise your ceiling more than a pay rise would. The page tells you which one held you back for exactly this reason.
• Confusing the loan with the price. The output is a loan amount. The price you could consider is that loan plus your deposit, and buying costs sit on top of both.
• Stretching the term to buy more house. A longer term lowers the payment and raises the ceiling, but the property does not get cheaper. It simply costs more in interest.
• Budgeting nothing for the house itself. Maintenance, repairs, and furnishing arrive whether or not a ratio anticipated them. They are outside every lender formula on this page.

What this calculator leaves out: This calculator does not check your credit, verify income or employment, apply any specific lender’s overlays, model mortgage insurance, include closing costs, account for taxes or benefits, or reflect country-specific programme rules. It applies the ratio percentages you choose to the figures you enter. A lending decision comes only from a lender.

Frequently asked questions