The Three Values Every Owner Needs to Know
What is my diamond actually worth?
There is no single answer, and that is not evasion. The same stone, on the same day, has three different legitimate values depending on why you are asking. People run into trouble when they use one of those numbers for a purpose it was never meant for — insuring against a probate figure, or expecting a jeweller to hand over the amount printed on an insurance certificate.
This page explains what the three values are, why they differ so much, where VAT sits in each of them, and what actually drives the number underneath all three.
The three values, briefly
| What it answers | Roughly | |
|---|---|---|
| Insurance | What would it cost to replace this with an equivalent new stone, at retail? | The highest figure |
| Probate | What would it realistically sell for, second-hand, on a given date? | Around 35–55% of the insurance figure |
| Resale | What will a trade buyer actually pay me for it today? | Around 25–50% of retail |
Take a one carat round brilliant, G colour, VS1 clarity, excellent cut, with a GIA report. In the current UK market that stone sits at roughly £4,000 to replace new. Its open market value for probate is somewhere near £1,800. If you walked into a dealer tomorrow, you would be looking at something closer to £1,200.
Same stone. Same day. All three numbers are correct.
Why the gap is so wide
The instinct is to assume the stone has lost value. Usually it hasn’t. What you are seeing is the retail structure coming off — and a meaningful part of that structure is tax.
When a diamond is bought at retail, the price includes far more than the stone: the shop, the staff, the marketing, the warranty, the box, the margin, and VAT. None of that is recoverable by a private seller. A dealer buying your diamond has to sell it on at a profit, so they are pricing from the wholesale end, not the retail end. The stone itself may be worth exactly what it always was — you are simply now on the other side of the counter.
Where VAT sits in each of the three numbers
This is the part almost nobody explains, and it accounts for a surprising slice of the difference.
Insurance: the figure includes VAT
Jewellery and diamonds are standard-rated in the UK, so a retail price carries VAT at 20 per cent. That means roughly one sixth of any retail figure is tax. On our £4,000 example, about £667 of it is VAT and never belonged to the stone at all.
This is correct for insurance purposes. If you had to replace the piece you would walk into a shop and pay VAT like anyone else, so the replacement figure should include it. But it explains a good part of the drop the moment you move to any other basis.
One practical trap: some UK diamond retailers advertise prices excluding VAT. If you are using a website to sense-check what your stone would cost to replace, check which figure you are looking at, or you will understate your cover by a sixth.
Probate: the figure excludes the buyer’s premium and the VAT on it
For inheritance tax, open market value at the date of death is measured by what the item would fetch on the open market — in practice, the hammer price at auction. HMRC’s guidance is specific that this means the gross sale price before commission is deducted, and without the buyer’s premium added on top.
That matters, because a single auction transaction produces three quite different numbers:
- What the buyer pays. Buyer’s premiums commonly run at 25 to 30 per cent, with VAT charged on the premium. A £1,000 hammer price can cost a buyer somewhere around £1,300.
- What the estate receives. After the seller’s commission, again with VAT on it, the estate might see closer to £775.
- What HMRC uses. £1,000 — the hammer price, in the middle.
So the probate figure is neither what a buyer hands over nor what the estate banks. It sits between the two, and the VAT flowing through the saleroom’s fees forms no part of it.
Getting this wrong in either direction has consequences. Using a VAT-inclusive retail figure inflates the estate and can mean paying inheritance tax that was never owed. Using the net proceeds figure understates it, and HMRC can treat careless undervaluation as negligence.
Resale: you charge no VAT, but the buyer’s VAT position shapes the offer
When you sell a diamond as a private individual you are not VAT-registered, so there is no VAT on that sale. Straightforward enough.
What is less obvious is how the dealer’s VAT position affects what they can offer you. Because they cannot reclaim any VAT on a purchase from a private seller, selling it on under normal VAT rules would mean handing HMRC a fifth of the full sale price with nothing to offset it. Instead, most second-hand jewellery moves under the VAT margin scheme, where the dealer accounts for VAT only on the difference between what they paid and what they sell it for — one sixth of the margin, rather than one sixth of the price.
That scheme is what makes trading pre-owned jewellery viable at all. It also means the dealer’s margin has to carry that VAT, which is one of the reasons buy-in offers sit where they do.
If you are buying second-hand rather than selling, the same scheme is why you will see a single gross price with no VAT broken out, and why you cannot reclaim VAT on it.
One other tax worth knowing about
If you inherit a diamond and later sell it for more than its probate value, the gain can fall within capital gains tax. There is an exemption for tangible moveable property sold for £6,000 or less, and particular rules for items forming a set. Most inherited jewellery never comes near this, but if the piece is substantial it is worth asking an accountant before you sell rather than after.
VAT and capital gains treatment depends on your circumstances. This page is general information, not tax advice.
→ Read more: Why your insurance valuation is double the probate figure
What actually drives the number
Most explanations stop at “the four Cs”. That is true but not very useful, because the four Cs do not carry equal weight and they do not behave in a straight line.
Carat weight moves in steps, not smoothly
Diamonds are not priced by the gram. The trade prices from bands — one bracket for stones between 0.90 and 0.99 carats, another for 1.00 to 1.49, and so on. Crossing a band boundary produces a jump.
This is why a 0.99 carat stone can be worth noticeably less per carat than a 1.00 carat stone that looks identical to the eye. Buyers pay a premium to cross a round number, and cutters will sacrifice proportions to stay above one. If your stone sits just under a threshold, that matters.
Colour and clarity interact
A single colour grade is worth far more at the top of the clarity scale than at the bottom. In the current UK market, dropping from D to F colour costs around a quarter of the value in a flawless stone — but the same two-grade drop in a heavily included stone barely registers.
The practical version: in a very clean stone, colour is where the money is. In a lower-clarity stone, chasing colour is largely wasted.
Cut is the one most people underrate
Cut is the only C that is about workmanship rather than nature, and it does more for how a diamond looks than anything else. Moving from Excellent to Very Good typically costs 10 to 15 per cent. Below that, the drops get steeper and start to be visible.
One wrinkle worth knowing: GIA only issues an overall cut grade for round brilliants. Ovals, cushions, emeralds and the rest have no graded cut, which makes them harder to value confidently and is part of why fancy shapes generally trade below round for the same specification.
The laboratory on the certificate changes the price
Two stones with identical grades on paper are not worth the same if those grades came from different laboratories. GIA is the trade’s reference point. An IGI-graded natural stone typically trades some 12 to 19 per cent below an equivalent GIA one, and softer laboratories trade at a steeper discount still, because their grades are widely regarded as more generous.
A stone with no report at all carries the biggest discount of the lot — not because it is worse, but because nobody can verify what it is.
→ Read more: How to read your diamond certificate
Fluorescence cuts both ways
Around a third of diamonds glow under ultraviolet light. In colourless stones — D to F — strong blue fluorescence is discounted, sometimes heavily, because it can occasionally give a stone a hazy look. In warmer stones from K downwards, the same blue glow can make the diamond face up whiter, and the market will occasionally pay a small premium for it.
So “does it fluoresce?” is the wrong question. “Does it fluoresce, and what colour is the stone?” is the right one.
→ Read more: Why two diamonds that look identical sell for very different prices
Natural or laboratory-grown
This makes a bigger difference than everything above combined.
Laboratory-grown diamonds are chemically and optically identical to mined ones, and they cost a small fraction of the price — typically 10 to 20 per cent of an equivalent natural stone, with prices still falling year on year as production expands.
The consequence for value is stark. Because new lab stones keep getting cheaper, second-hand ones have very little market. Some jewellers decline to buy them back at all. If you have a lab-grown diamond, insure it for what it would cost to replace, but do not plan around a resale figure.
If you are not sure which you have, the certificate will say. Reports issued for lab-grown stones state it explicitly.
Which number do you actually need?
You are insuring it. You want replacement value, VAT included, and you want it current. Insurance valuations date quickly — metal and stone prices move, and an old figure can leave you underinsured at exactly the wrong moment.
→ Read more: Underinsured jewellery: what happens when you claim
You are dealing with an estate. You need open market value at the date of death, the basis HMRC requires under section 160 of the Inheritance Tax Act 1984. Any single item worth £1,500 or more must be listed individually on schedule IHT407.
→ Read more: Valuing jewellery for probate: an executor’s guide
You are thinking of selling. You need to know what the market will actually pay, which is the least comfortable of the three numbers and the one most worth knowing before you start. Where you sell changes the figure significantly.
→ Read more: Where to sell a diamond in the UK
You have just inherited something. Start by finding out what you have before deciding anything. Cleaning, repairing or splitting up pieces before they are valued can cost real money.
→ Read more: I’ve inherited a diamond ring — what do I do first?
Get an estimate for your stone
The calculator on this page takes what you know about your diamond and returns all three figures at once, with the working shown.
Four details are essential: carat weight, colour, clarity and cut. Everything else is optional, but each additional detail narrows the range — the certificate number, the measurements in millimetres, the fluorescence grade, and which laboratory graded it. The tool shows you how much each missing detail is costing you in accuracy, so you can decide whether it is worth digging out the paperwork.
If you have the grading report to hand, use it. Estimating from memory produces a much wider answer.
Where an estimate stops being enough
An automated figure is a starting point. It tells you roughly where you stand and whether the thing in front of you is worth taking further. It cannot examine the stone.
Bring in a qualified valuer when the figure is substantial, when you are dealing with probate and any item might reach the £1,500 reporting threshold, when the piece is antique or signed, or when a decision of real consequence rests on the number. Look for RICS, the Institute of Registered Valuers, or the National Association of Jewellers, and ask for the basis of value to be stated in the report — a valuation that does not say whether it is a replacement or open market figure is of limited use.
The difference between an estimate and a valuation is not precision. It is that someone qualified has held the stone and put their name to the number.
Market figures on this page reflect UK prices during 2026 and are indicative. Diamond prices move; treat any figure here, including the calculator’s, as an estimate rather than a valuation. VAT and tax treatment depends on individual circumstances — take professional advice before acting on any figure.