Rate used to anchor the value: pure gold (24 carat) around €120/g in mid-July 2026, so 18-carat gold sits around €94/g for the metal value, and closer to €78/g as a buyback price. The rate moves every day — check it for the date you're reading.
You've got a piece of gold in a drawer, you're wondering what it's worth, and you do what everyone does: you type "gold estimate online" and land on a calculator. You enter the weight, pick "18 carat", click, and there it is — a value on the screen. Fast, free, looks legit. But before you take that figure at face value, there's one plain thing to understand: who built that calculator, and what it's actually working out.
The problem: the site valuing your gold is the one that wants to buy it
Look closely at the page you're on. Nine times out of ten, the estimate tool belongs to a buyback counter, a refiner or a gold dealer. Their business is to buy your gold to resell or melt it. So the figure their tool shows you isn't "the value of your jewellery" — it's the price at which they're willing to buy it from you. And a buying price, by definition, sits below the metal value, otherwise they'd make nothing.
It's exactly the same trap as the counters in town, except here it's dressed up as a neutral calculator. You think you're reading a thermometer; you're actually reading a purchase offer. It isn't dishonest in itself — a buyer is entitled to a margin — but it's misleading if you take their estimate as the "true" value of your gold. Me, I've got nothing to buy off you: my thing is the price per gram, full stop. So let's see what these calculators work out, and how to get back to the figure you actually care about.
How an estimate calculator works (and where it loses you)
The base maths is simple, and it's the same everywhere: weight × purity × the day's gold rate. A 5-gram piece in 18 carat is 5 × 0.750 = 3.75 grams of pure gold. If pure gold is at €120/g, the metal in your piece is worth around €450. So far, any honest tool would give you roughly the same.
Where the calculators diverge is the percentage of the rate they apply. A buyback counter doesn't pay you 100 % of the metal value: it takes a margin. On the small quantities a private seller brings in, that margin often sits around 10 to 20 %, and the gap between a fair buyer and a greedy one can reach 20 to 30 %. Refiners buying in bulk run closer to the rate (2 to 5 % margin), but they're not the ones dealing with you and your single chain.
Concretely, for the same gram of 18-carat gold in mid-July 2026:
- ~€94/g = the metal value at the day's rate (what your gold actually weighs in)
- ~€78/g = a typical buyback price shown by a counter's calculator
- and sometimes a fair bit less if the buyer applies a heavy margin or "fees"
The calculator isn't lying about the weight or the rate. It "lies" by omission about the nature of the figure: it calls "estimate" what is really its own purchase price.
The biases to know before you click
Beyond the fact that the calculator is judge and buyer in one, there are three recurring traps.
The "buyback price" presented as "value." This is the core bias. If you want to sell, the buyback price is the relevant figure — but always compare it to the metal value to see what percentage of the rate you're really being offered. If you want to buy, or simply know what a piece is worth, that number doesn't answer your question.
The carat is assumed, not checked. The calculator makes you pick "18 carat" from a dropdown. But it can't see your piece: it takes your word for it. If it's actually 9 carat, gold-plated or unhallmarked, the estimate is wrong from the start. The tool calculates cleanly from a figure nobody verified.
Huge gaps from one site to the next. Run the test: enter the same piece (same weight, same carat) into three different calculators. You'll get three figures that can vary by 20 to 30 %. That alone tells you none of them is "the" reference — they're commercial offers, not an official quote.
An estimate calculator isn't a thermometer, it's a shop window. It tells you the price the site wants to buy your gold at — not what your gold is worth.
The method to check it yourself (and stop depending on them)
The good news is you don't need anyone to do the honest sum. You need three things: the weight (a small kitchen scale to the gram is enough for a first idea), the purity (the hallmark — the eagle's head for 18 carat in France, or "750") and the day's gold rate (free everywhere online).
Then: weight × purity × pure-gold rate. An 8 g chain in 18 carat, with pure gold at €120/g, gives 8 × 0.750 × 120 = €720 of metal. There's your real reference. From there, everything becomes readable:
- If a buyer offers you €560, that's about 78 % of the metal — up to you to judge whether that works.
- If a shop sells you the same chain for €1,400, you know you're paying roughly double the metal: that's the workmanship and the margin, not the gold. (I go into it in why new jewellery costs 2 to 3 times the gold price.)
And if you doubt the purity itself — the real weak point of any estimate — that's when you have to step out of the virtual: check the hallmark, and get it certified if needed. I've written the steps in testing gold at home before buying second-hand and what the eagle's head hallmark really guarantees.
What I do, myself, with these calculators
I use them, but as a starting point, never as a verdict. When I look at a piece, my first question isn't "what will they buy it for", it's "how much gold is in there, at today's rate". Once I've got that number in my head, any online estimate becomes readable: I can see straight away what percentage of the rate I'm being offered, and whether it's a fair deal or a polite rip-off.
For my daughters, I keep a little log of weight + date + price for every piece I buy — so the day I want to measure the gain, I won't have to trust a buyer's calculator: I'll have my own figures. That's the whole idea: don't let the one who wants to buy your gold also be the one who decides what it's worth. And when the goal is to buy at the right price rather than sell, a buyer's estimate is useless — you need to compare the real price per gram, shop by shop.
Eleven second-hand 18-carat gold shops, normalised per gram — to gauge a piece's real value without going through a buyer's estimate.
To wrap up
Online estimate calculators aren't crooks, but they aren't neutral referees either: they're tools built by people who want to buy your gold, and the figure they show is their purchase price. Keep them as a marker, never as the truth. The real value, you can work out yourself in thirty seconds: weight × purity × the day's rate. The rest — sell, keep, buy — that's your call, with your situation. I'm just giving you enough to stop signing with your eyes shut.
Sources for the figures cited:
- 18-carat gold price per gram (≈€78.63/g buyback, ≈€93.66/g metal value, pure gold ≈€120/g, 17 June 2026): veracash.com and goldavenue.com, accessed 17 June 2026
- How an estimate is calculated (weight × purity × rate) and how buyback calculators work: lingor.fr and gemmor.fr, accessed 17 June 2026
- Counter margins (10-20 %) vs refiners (2-5 %) and 20-30 % gaps between buyers; advice to compare at least 3 offers and ask for the percentage of the rate: leguidedubijou.fr, accessed 17 June 2026