There is a number that gets repeated every time engagement rings come up in conversation, and it is almost always wrong.

The old rule was two months salary, invented by an advertising agency in the 1930s and repeated so often that people mistake it for tradition. It has no basis in anything except a campaign brief, and following it in 2026 would mean ignoring the largest change to diamond pricing in half a century.

Here is what actually determines the cost of an engagement ring in Australia, and where the money goes.

The market has genuinely changed

Two developments have reshaped pricing, and neither has fully filtered through to how people shop.

The first is the collapse of lab-grown diamond prices. Laboratory-created stones are chemically and physically identical to mined diamonds, and when they entered the mainstream a decade ago they sold at a modest discount. That discount is now a chasm. Production capacity in India and China has expanded enormously, average prices have fallen by 20 to 30 per cent against 2024 alone, and some categories have dropped by more than 90 per cent from their peak. Lab-grown stones above a carat now commonly sell for somewhere between 5 and 10 per cent of a comparable natural diamond.

The second is a change in how those stones are graded. In late 2025 the Gemological Institute of America stopped assigning lab-grown diamonds the familiar D to Z colour scale and the flawless to included clarity scale it uses for natural stones. Lab-grown diamonds now receive one of two descriptive categories, premium or standard.

That is a significant shift and it matters for buyers. The industry's most respected laboratory has formally stopped treating the two products as comparable, which means the old habit of comparing a lab-grown stone and a natural stone on identical specifications no longer works the way it did.

What this means for your budget

The practical consequence is that you now face a genuine fork rather than a sliding scale.

Choose a lab-grown stone and your money buys dramatically more carat weight. A budget that would have bought a modest natural stone will buy something several times larger. If visual impact per dollar is the priority, nothing else comes close.

Choose a natural stone and you are buying scarcity, and you should be clear-eyed that this is what you are paying for. Natural diamonds retain some resale value. Lab-grown diamonds, in practical terms, do not, because supply is effectively unlimited and the secondary market is close to non-existent.

Neither choice is wrong. What is wrong is making the choice without understanding it, or worse, being sold a lab-grown stone at natural-stone pricing by a retailer relying on the customer not knowing the difference.

Where the money actually goes

Strip a ring back and the cost sits in four places.

The centre stone is usually 50 to 70 per cent of the total on a diamond ring. Everything about the stone moves this number, and not evenly.

The metal is a smaller component than most people expect. Platinum costs more than gold and is heavier and more durable. Eighteen carat gold is 75 per cent pure and holds detail better than nine carat, which is 37.5 per cent gold and noticeably harder. White gold is yellow gold alloyed and rhodium plated, and that plating wears and needs redoing every few years. Nobody mentions this at the point of sale often enough.

The setting and labour vary enormously. A solitaire in a simple four-claw setting is a fundamentally different amount of bench work from a micro-pave halo with a hidden diamond under the basket. This is where handmade and mass-produced diverge most sharply.

Retail overhead. A shopping centre chain carries rent, stock financing and a sales floor. A small studio carries a workshop. That difference is real and it shows up in the price of identical stones.

The four Cs ranked by importance

The four Cs are cut, colour, clarity and carat. They are presented as equally weighted. They are not.

Cut is the one that matters most and gets the least attention. Cut is not the shape, it is the quality of the proportions and the polish, and it determines how the stone handles light. An excellently cut diamond with middling colour will outperform a poorly cut stone with superb colour every time, in any lighting, to any observer. If you compromise anywhere, do not compromise here.

Carat is what most people over-weight. Prices jump at the round numbers because demand jumps there. A stone at 0.90 carat costs meaningfully less than one at 1.00 carat and the difference is essentially invisible on a hand. Buying just under a threshold is the single most effective way to save money without a visible compromise.

Colour matters up to a point. The scale runs from D, entirely colourless, down through the alphabet. Beyond about G or H, most people cannot detect any warmth without a comparison stone alongside. Paying a premium for D when H looks the same in the ring is spending on a certificate rather than on the ring.

Clarity matters least. The relevant question is whether inclusions are visible without magnification. A stone graded VS2 or SI1 is typically clean to the naked eye and costs substantially less than a flawless stone that looks identical on a finger.

The general rule that serves most buyers well: prioritise cut, accept G or H colour, accept eye-clean clarity, and put the savings into a stone that is cut properly.

Certification is not optional

Any natural diamond of significance should come with an independent laboratory report, and the two names that carry weight internationally are GIA and AGS. The report documents the stone's characteristics so you can compare across retailers rather than taking a shop's word for its own grading.

In-house certificates issued by the seller are not the same thing, for the obvious reason.

For coloured diamonds the report also establishes whether the colour is natural, treated or laboratory-grown, which is the single largest determinant of value in that category.

The Australian specifics

A few things differ here from the international advice that dominates search results.

Hallmarking is not compulsory in Australia in the way it is in the United Kingdom, so metal purity marks are applied voluntarily rather than by law. Buy from someone who stands behind their own marking.

GST applies at 10 per cent and should be included in a quoted retail price.

Insurance requires a valuation, and a valuation is a separate document from a grading certificate. Get both. Valuations also need updating periodically, because a ring insured at a 2019 valuation is underinsured today, particularly if it contains anything Australian.

That last point deserves expanding, because it involves the one part of the diamond market where Australia genuinely leads the world.

The Argyle exception

The Argyle mine in the East Kimberley produced more than 90 per cent of the world's pink diamonds until it closed permanently in November 2020. Rio Tinto's final tender of remaining inventory concluded in October 2025, which makes 2026 the first year in which every Argyle pink diamond changing hands comes from the secondary market.

Supply is now fixed and can only shrink. Prices have responded accordingly, with documented appreciation of roughly 8 to 12 per cent a year since closure and stones carrying Argyle provenance commanding a premium of 20 to 50 per cent over comparable pinks from elsewhere.

For an Australian buyer this is worth knowing for two reasons. If a ring in your family contains Argyle material, it is probably insured for a fraction of what it is now worth. And if you are considering a coloured stone, the paperwork matters more than anywhere else in jewellery: the laser inscription, the Argyle certificate and lot number, ideally alongside a GIA report confirming natural colour origin.

Bespoke versus off the shelf

Custom making is generally assumed to be the expensive option. Frequently it is not.

When a ring is made to order, you pay for the stone you chose and the metal actually used, without financing a display case full of unsold stock. The workshops doing this work in Australia tend to be small studios rather than chains, which means lower overhead recovery in the price.

What custom work does cost you is time. Expect several weeks from design to finished ring, longer if you are sourcing a particular stone. Couples who leave it until three weeks before a planned proposal end up buying from stock, which is how a lot of people end up with a ring that was nobody's first choice.

It also opens options that stock cannot. Resetting a family stone. Working around an unusual finger size. Matching a wedding band to a ring that already exists.

Perth is a reasonable illustration of how the local end of this market works, with several established studios making to order rather than retailing stock. Looking at what a workshop like Stelios Jewellers shows among its engagement rings Perth couples commission gives a fair sense of what bespoke pricing actually buys compared with the equivalent from a chain, which is a more useful comparison than any published average.

The timeline nobody plans for

Cost is not the only thing people underestimate. Time is the other.

A ring bought from stock can be bought today. A ring made to order runs to several weeks, and longer again if a particular stone has to be sourced from overseas or if a coloured stone with the right paperwork has to be found.

Sizing adds more. A ring sized incorrectly needs adjusting after the proposal, which takes the ring away for a period nobody anticipated. Some settings cannot be sized at all, so the measurement has to be right at the start rather than corrected later.

Then there is insurance. Most home and contents policies cap jewellery cover at a modest figure per item unless the piece is specified separately, and specifying it requires a valuation. A ring collected on Friday and proposed with on Saturday has spent a weekend uninsured, which people only think about afterwards.

The practical advice is to start three months before the date you have in mind. That is long enough to have stones sourced, a design resolved, the ring made properly, sizing confirmed and insurance arranged without any of it being rushed.

What happens after you buy

A ring is a worn object and it needs occasional attention, which is worth budgeting for from the start.

Claw settings loosen over years of ordinary wear and should be checked periodically. A loose claw noticed at a check costs nothing. A stone lost because nobody looked costs the stone.

White gold needs rhodium replating every few years as the plating wears through to the slightly yellow alloy underneath. Platinum does not need plating but develops a soft patina, which some people prefer and others have polished off.

And valuations need updating. A ring insured at its 2019 valuation is underinsured today, particularly if it contains natural coloured stones.

Questions worth asking before you buy

Is this stone natural or laboratory-grown, and can I see the report? After the GIA grading change, do not assume the certificate format tells you.

What is the cut grade? If the answer is vague, so is the ring's performance.

Is the stone eye-clean? Ask them to show you, not tell you.

Is white gold rhodium plated, and what does replating cost? It will need doing.

What is the resizing allowance? Some settings, particularly full eternity bands and channel settings, cannot be resized at all.

Is there a valuation for insurance, and is it separate from the grading report?

What is the warranty on the setting, and does it cover stone loss?

The honest answer on cost

There is no correct number. There is a stone that suits the person wearing it and a budget that does not create stress at the start of a marriage, and the skill is matching those two things.

What has changed is that the budget now stretches much further than it did five years ago, provided you understand what you are buying. Prioritise cut over size, buy just under the carat thresholds, insist on independent certification, and be clear on whether you are buying a natural stone or a laboratory-grown one.

Do that and the two months salary rule can go back where it came from, which is an advertising brief from the Depression.

This article is general information only and does not constitute financial or investment advice. Diamond prices and grading standards change. Confirm current specifications and certification with your jeweller.