Family Guarantee Home Loans: What the Guarantor Really Carries

On a $750,000 purchase with a 5% deposit, a family guarantee puts $112,500 of your parent's home on the line and saves you about $33,488 in lenders mortgage insurance. Both numbers are real, and almost no guarantor guide prints them next to each other. The guarantee is roughly three times the cost it avoids, and that ratio is the honest starting point for the conversation, not the LMI saving on its own.

What is a family guarantee?

A relative, almost always a parent, pledges equity in their own property as additional security for your loan. No cash changes hands. They do not appear on your title and they make none of your repayments. What the lender gains is a second property to secure part of the debt, which pulls your effective loan-to-value ratio down to 80% and removes the LMI requirement that applies above it. What your parent gains is nothing, financially. This is a favour with a number attached, and the number is worth stating out loud.

How is the guaranteed amount calculated?

It is the slice of your loan sitting above 80% of the purchase price:

limited guarantee = (purchase price − your deposit) − 80% of purchase price

So a $750,000 purchase with $37,500 down gives a $712,500 loan, of which $600,000 sits inside the 80% threshold. The remaining $112,500 is the guarantee. Your parent's liability is capped there. It is not the whole loan, and a guarantee that is not capped at a stated dollar figure is a different and much worse instrument.

Every extra dollar of your own deposit reduces the guarantee by a dollar. Saving another 5% of the price is the most direct way to shrink what a parent carries.

Is a limited guarantee the same as being a co-borrower?

No, and the distinction is the whole point of the structure. A co-borrower is liable for the entire debt and their income is assessed alongside yours. A limited guarantor is liable only up to the capped figure, and only if you default and the sale of your property fails to clear the loan. An unlimited guarantee sits between the two and exposes them to the full principal, interest and the lender's recovery costs. Most lenders now default to the limited form, but the word to check for in the documents is the cap, expressed as a dollar amount, not a percentage or a description. If nobody can point to that figure on the page, the arrangement has not been explained properly, and that is the moment to stop rather than the moment to sign.

How much equity does the guarantor need?

Enough that their own loan-to-value ratio stays below 80% after the guarantee is registered against their property. On a $650,000 purchase needing a $97,500 guarantee, a parent with a $700,000 home and nothing owing has $560,000 of headroom to their own 80% line, so the guarantee fits comfortably. The same parent carrying a $200,000 mortgage still has $360,000 of headroom. The constraint bites where the guarantor's own mortgage is large relative to their property, which is worth checking before anyone gets attached to a purchase price.

When does the guarantee end?

When your own loan-to-value ratio reaches 80% without their security, which happens through repayments, price growth, or both together. Lenders commonly see release at three to seven years. At a flat valuation on that $750,000 purchase, your loan has to fall from $712,500 to $600,000, a reduction of $112,500, which is a decade of scheduled principal on a typical thirty-year term and considerably faster with either overpayments or growth. Release is not automatic. Somebody has to apply for it, and the property is usually revalued.

What does it cost the guarantor beyond the risk?

One consequence is routinely missed until it bites. The guaranteed amount is treated as a contingent liability when the guarantor is next assessed for credit of their own. A parent who plans to refinance, buy an investment property or downsize within a year or two may find their borrowing capacity reduced by the guarantee they gave you. Raise that timing before the application goes in. They also pay for their own independent legal advice, which most lenders require and which is a genuine safeguard rather than a formality.

Is there a way to avoid risking a family home?

Often, and it deserves checking before the family conversation rather than after. The federal First Home Guarantee lets eligible first home buyers purchase on a low deposit without paying LMI, with the government carrying the guarantee instead of a relative. No family property is mortgaged, there is no second set of legal fees, and no contingent liability lands on your parents' future borrowing. One caution on the detail: eligibility, income tests and property price caps have moved recently, and the Australian broker sources consulted for this article disagree about the current position, with some describing income caps as removed and others as still applying. That disagreement is itself a reason to check with Housing Australia rather than any summary. Where the scheme does fit, it delivers the same LMI outcome without putting a house at risk, and any guarantor discussion should start by ruling it out. For what the premium would otherwise be, see LMI cost by deposit size.

A note on the figures

Guarantee amounts were computed from the 80% loan-to-value threshold rather than taken from a lender summary, and the calculation reproduces a published worked example exactly: a $750,000 purchase at a 5% deposit gives a $712,500 loan and a $112,500 guarantee. LMI figures are indicative only, since premiums vary by lender, insurer, deposit and loan size, so treat the comparison as an order of magnitude and use the LMI calculator for your own numbers. Structure details were checked on 10 August 2026 against Australian lender and broker sources that agree on the limited-guarantee form, the release condition and the independent legal advice requirement. Confirm the First Home Guarantee caps and eligibility with Housing Australia, since those change.