The real cost of overpaying by 5%

Most buyers treat overpayment as a rounding error. You find the property, the campaign runs hot, and paying a little above plan feels like the price of getting it done. Five percent over. You'll make it back.

You won't, and the reason is that the number on the contract is not the number you pay.

On an $800,000 purchase, 5% is $40,000. Hold the property for ten years and that $40,000 costs you close to $79,000. Almost half of that never appears on a statement, which is precisely why so few buyers run the numbers before they sign.

Here is the working.

Two buyers, one number apart

Take an investment-grade property with a true market value of $800,000. One buyer holds the line and pays $800,000. A second buyer, caught in the campaign, pays 5% over at $840,000.

Both borrow at 80%. Both intend to hold for ten years. The only difference between them is $40,000 at the point of sale.

First, the $40,000 buys nothing

The property is worth $800,000. That is what an independent valuer sees, what the next buyer will pay, and what the market will grow from. Pay $840,000 and you have not acquired $40,000 of anything. You own an $800,000 asset and you are $40,000 lighter.

The important part is what the bank does next, because this is where most modelling of overpayment gets it wrong.

Lenders do not advance 80% of whatever you agreed to pay. They advance 80% of the lower of the contract price and the valuation. Both buyers here are lent the same $640,000, because the property values at $800,000 for both of them. The overpayer does not get to borrow their way over the gap. They fund all $40,000 of it in cash, on top of the deposit they had already budgeted.

That is a valuation shortfall, and in a softening market it is not a rare event. The bank does not share your enthusiasm for the property. Running total: $40,000, all of it cash.

Second, the duty rides along

Stamp duty is charged on what you pay, not on what the property is worth. Lift the price by $40,000 and the dutiable value lifts with it. At the marginal rates applying around this price band, that is roughly $2,000 in additional duty, varying by state.

Nobody negotiates their stamp duty. They negotiate the price, and the duty follows wherever the price goes.

Running total: $42,000.

Third, and largest, the time

This is the layer that does the real damage, and the one almost every version of this analysis understates.

The overpayer walks away from settlement $42,000 of cash worse off. That money does not sit still for ten years waiting to be counted. Held in an offset account against the loan, $42,000 saves interest at the loan rate, every year, on a balance that keeps growing because each year's saving reduces the next year's interest. That is not a forecast. It is compounding, and it runs whether you think about it or not.

At 6.5%, below the average variable investor rate and close to what a well-priced interest-only investment loan actually costs today, $42,000 held for ten years is worth $78,840.

Note what that rate is doing. Interest saved in an offset account is not taxable income, so there is no deductibility argument to have and no tax haircut on either side of the comparison. This is a clean number.

Running total: $78,840.

The number that matters

Forty thousand dollars of overpayment. Just under $79,000 of real cost across a ten-year hold.

Every dollar overpaid at the contract costs you $1.97 by the time you sell. The visible premium was 5% of the purchase price. The real premium, once duty and time are counted, is 9.9%. You did not pay 5% over. You paid very close to 10% over, and $38,840 of it was never on the contract.

And $78,840 is the floor, not the ceiling. It assumes the $42,000 does nothing more ambitious than sit against your own debt. For most investors, $42,000 is a meaningful share of the cash required for the next purchase, which means the true cost is not only the money. It is the acquisition that gets pushed out by a year or two, and everything that would have compounded inside it.

Why this is a worse time than usual to be wrong

There is a version of this mistake the market forgives. In a rising market the overpayer is carried up with everybody else, and time papers over the entry price.

This is not that market. National dwelling values fell 0.7% in July 2026, the largest single-month decline since December 2022. The falls have been sharpest at the top: upper-quartile values fell 3.2% nationally over the three months to July, while lower-quartile values rose 0.3%. That gap is a credit-capacity story. Larger loans lose more borrowing power as rates hold, so the premium end reprices hardest, and the premium end is exactly where a lot of investors are shopping.

An overpayer today does not start level and wait for growth. They start behind true value, in a segment already moving against them, having tipped in an extra $42,000 of cash that the bank declined to lend them.

Growth compounds on what a property is worth, not on what you paid. Overpay and you have started the race $40,000 back and handed the market a head start it did not need.

The part nobody puts in the pitch

Ask why overpayment is this common when the arithmetic is this plain, and the answer is usually about incentives rather than ignorance.

Look at how most buyers are represented. A buyer's agent charging a percentage of the purchase price earns more every time you pay more. Their fee on $840,000 exceeds their fee on $800,000. The single number they are engaged to push down is the same number their own pay rises with. Add a model measured in deals settled rather than dollars saved, and "just go a little higher to secure it" stops reading as a failure.

This is not a claim about any individual agent, and plenty of them do excellent work despite the structure rather than because of it. It is a claim about the structure. When the fee rises with the price, nobody in the room is paid to protect your ceiling.

What we do differently

CQB Partners works on a flat fee. It does not move whether you buy at $800,000 or $840,000, which means we have exactly one job at the negotiating table: get your number down and keep you from paying a premium. Our fee is fixed. What you save is not, and it is yours.

On the engagements we have completed to date, that saving has exceeded our fee, in most cases by several multiples. We measure it by benchmarking the price our client actually paid against an independent third-party valuation estimate for the property, and the exact basis varies from deal to deal depending on what the property and the campaign allow.

We are not going to turn that into a guarantee. Too much depends on the asset, the campaign, the vendor and the market on the day, and a firm promising you a fixed multiple is promising you something it does not control. It is a record, not a forecast. What we will say is that our incentive and yours point the same way, which is more than the percentage model can claim.

So the question is worth asking plainly. Why pay more? More for the property, and more for representation that is rewarded when you do.

The most useful first move in property is not a purchase. It is a number: the most this asset is worth to you, set with rigour and defended by someone with no reason to let it drift.

That is the conversation to have first.

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This article is general information prepared by CQB Partners, a licensed buyer's agency operating Australia-wide. It is not financial advice and does not take account of your objectives, financial situation or needs. All figures are illustrative modelling based on the stated assumptions and market data current as at August 2026. They are not a forecast, a projection of your own outcome, or a recommendation. Individual costs, lending criteria, tax treatment and stamp duty vary by state and by circumstance. Consider your own position and seek appropriately licensed advice before making any investment decision.