Every card on champ. shows two prices when a saving exists: the champagne stone's own price, and a struck-through figure for what a similar near-colourless diamond costs. The chip beside it is the difference — the champagne discount. This page is the full account of how that figure is produced, because a comparison you cannot check is not worth showing.
What "similar" means
Each stone is matched against natural, GIA-graded diamonds of colour G or H — the near-colourless range most people buy — that share its shape, its clarity grade and its cut, and sit within a narrow carat window. The window is ±8% of the stone's weight, widened to ±15% only if fewer than eight matches exist, and it never crosses a trade price threshold (0.50, 0.70, 0.90, 1.00, 1.50, 2.00, 3.00 carats and so on), because price per carat steps up at each of those and a window that straddled one would average two different markets.
Cut is compared on the GIA scale — Excellent, Very Good, Good. Retailer sub-grades such as Ideal, Super Ideal and Rare Carat Ideal are GIA Excellent stones with extra curation, so they match against Excellent. That slightly understates the saving on a Super Ideal stone, which is the safe direction.
Why the struck price is the lower quartile
From the matched stones we take price per carat, find the lower quartile — the point a quarter of them fall below — and scale it to the champagne stone's weight. Not the median, and not the cheapest listing.
The question a shopper is really asking is what would a similar white stone cost me, and across tens of thousands of listings from more than one retailer that means something near the floor, not the middle. The median would quote a struck price you could beat with a single search. The cheapest listing would let one mis-priced stone set the figure for everyone. The quartile is the conservative number an outlier cannot move. On this build, the same matched stones would have produced these savings under each choice:
| If the struck price were the… | median saving across the index |
|---|---|
| cheapest matching listing | 26% |
| lower quartile — what the site uses | 41% |
| median matching listing | 47% |
What is compared, and what is not
Matched: shape, clarity, cut, carat, colour range (G–H), origin (natural), and laboratory (GIA on both sides — the champagne stones are GIA by construction, so the GIA premium cancels rather than skewing the number).
Not yet matched: fluorescence, polish and symmetry. Strong fluorescence can move a white stone's price by several percent; that dimension is on the list.
When a card shows no comparison
Every stone is compared, but a comparison only appears as a saving. If a champagne stone costs more than its near-colourless equivalent — it happens, mostly with very small or unusually cut stones — the card shows its plain price and nothing else. Nothing is struck through to make a stone look cheaper than it is.
Where an exact match is too thin, the matching relaxes in steps that can only ever make the benchmark cheaper: any cut, then a clarity grade lower allowed, then two grades lower or smaller carats, then any clarity. A looser match can lower a struck price; it can never inflate one. Hovering any chip shows which step that stone used.
The numbers on this build
As of 2026-10-13
51,177 near-colourless G–H listings from Rare Carat and Ritani form the benchmark, refreshed weekly.
Of 2,822 champagne stones, 2,813 have a comparison, 1,981 of them from an exact match on shape, clarity and cut.
2,428 cost less than their near-colourless equivalent; the median saving among them is 44%.
A worked example from this build: a 3.22 ct Cushion, Fancy Brown Fancy Brown, VS2, Ideal cut, listed at $11,387. Its 30 matches — near-colourless G–H stones of the same shape, clarity and cut in the 3.00–3.48 ct window — put the lower quartile at $31,540, so the card shows $31,540 struck through and a −64% chip.
The matching itself runs every time the site is rebuilt, so a stone added tonight is compared on tonight's refresh. Retail prices for both champagne and white diamonds change daily; a figure here is a snapshot of the day it was built.