The Retailer Markup Leaderboard Methodology and What 110 Retailers Look Like Side by Side

Fourteen million diamond listings across 110 retailers. On a cert matched stone, the price spread between the cheapest and most expensive retailer stocking it simultaneously can be substantial. Real money, not rounding. And most buyers never see it because they open one website, find something they like, and buy.

That's the problem the CaratHunter diamond retailer markup leaderboard was built to solve. This is the methodology document. It covers how we identify matched stones, how we calculate each retailer's deviation, why we use the median, and where the data is thin enough that you should approach the ranking with appropriate scepticism. If you're here for the current quarterly rankings rather than the mechanics, the Q2 2026 leaderboard update has the live numbers.

Why category comparisons produce the wrong answer

Price comparison in the diamond market has a fundamental problem. Grade categories are too broad to be meaningful.

A "1.0ct G VS1 round" sounds specific. But two stones sharing those descriptors can diverge significantly on cut quality, fluorescence intensity, table percentage, depth ratio, girdle thickness, and polish and symmetry grades. All of those factors affect real world value. Compare retail prices across stones that share a grade bucket but differ on the specifics, and you're not measuring retailer markup. You're measuring variation between stones and calling it something else.

Cert matched stones eliminate the problem entirely. When the same stone, identified by its unique GIA or IGI certificate number, appears in two or more retailers' inventories at the same time, the comparison is genuine. The stone is physically identical. One retailer is charging more. Nothing is hidden by cut quality variance or specification ambiguity. The gap is the price gap and nothing else.

We cover the technical approach to identifying these cross-listed stones in our cross-retailer fingerprinting post. The short version: we match on certificate number first. Where certificates are absent or inconsistent between retailer feeds, we match on a combination of carat weight to two decimal places, colour grade, clarity grade, shape, and cut grade. Cert matched comparisons carry high confidence. Spec matched comparisons are included but flagged, and they carry lower weighting in the aggregate score.

The volume of cert matched stones across 110 retailers is large enough to matter. For the most popular categories, natural rounds between 0.5ct and 2ct and lab-grown rounds in the G to I colour range with VS1 to SI2 clarity, we have thousands of matched observations per quarter. For rarer categories and smaller retailers with narrower inventory, the counts are lower. We say so explicitly rather than obscuring it.

The markup calculation, step by step

For each cert matched stone where we have prices from two or more retailers, we calculate a cross-retailer median price. That's the midpoint price for that specific stone across all retailers listing it in the snapshot period.

We then calculate each retailer's deviation from that median for every matched stone in their inventory. If the cross-retailer median for a 1.3ct F VS2 round is $7,000 and a retailer lists it at $8,400, that retailer is 20% above median on that observation. A retailer listing the same stone at $6,300 is 10% below.

Every matched observation joins a retailer's pool for the quarter. At the end of the period, we take the median of all their per stone deviations. That single figure, the per retailer median deviation from cross-retailer median, is the leaderboard number. Positive means consistently above the market midpoint. Negative means consistently below it.

The choice of median over mean matters. Diamond price distributions are right skewed. A small number of very expensive listings, stones with unusual characteristics or genuine rarity premiums, would pull a mean upward and make a retailer appear more expensive than they actually are for a typical purchase. The median is resistant to those extremes. It represents the experience of a buyer purchasing a typical stone, not the experience of someone hunting a two-carat Type IIa with an exceptional origin report.

The choice of cross-retailer median as the benchmark also deserves explanation. External price models introduce their own assumptions and can lag real market movement. Wholesale benchmarks aren't consistently available across all categories. The cross-retailer median is fully transparent: it derives entirely from real listed prices at real retailers, updated each quarter, and can be interrogated in the underlying data.

We publish per category breakdowns where the dataset supports them: natural rounds, lab-grown rounds, natural fancy shapes, lab-grown fancy shapes. Some retailers specialise heavily in one segment. A blended overall figure for a retailer whose inventory is 90% lab-grown would mask whether they're actually competitive in that segment. Category level detail is documented in the full methodology note.

The scale of what we're covering

The retailers in the index range from platforms with millions of listings to boutique specialists. Not all of them contribute equally to the matched stone dataset, and coverage varies significantly.

Active listings by retailer across our top 15 by inventory size:

Rank	Retailer	Active listings
1	Yorxs	2,109,544
2	Adiamor	2,086,404
3	Taylor and Hart	1,880,535
4	Rare Carat	1,873,268
5	B2C Jewels	1,438,055
6	Loose Grown Diamond	1,433,241
7	Cape Diamonds	1,228,783
8	Brilliance	1,212,287
9	Brilliant Earth	789,270
10	Reve Diamonds	771,463
11	Novita Diamonds	707,660
12	Friendly Diamonds	707,612
13	RockHer	638,376
14	Moon Ocean	602,593
15	William & Sons Jewelers	564,148

Active inventory is not matched inventory. A retailer with two million listings from a proprietary wholesale feed may have fewer cert matched stones than a retailer with 600,000 listings sourcing from shared memo networks as its competitors. Listing counts tell you about market breadth. Matched stone counts determine leaderboard reliability.

The five largest retailers by listing count collectively hold more than nine million active listings. In popular natural round categories, that creates dense cross-retailer overlap. For a 1.0ct round in the G to I colour range and VS1 to SI1 clarity, we typically have matched observations across dozens of retailers simultaneously. The resulting median is stable and the retailer deviations from it are meaningful.

For smaller retailers or those specialising in categories not widely stocked elsewhere, matched counts can be low. We require a minimum threshold of observations before a retailer receives a numerical ranking rather than a "coverage insufficient" label. That threshold varies by category. The quarterly leaderboard tables show the matched observation count underpinning each retailer's score. It's the first number to check before acting on a ranking.

A worked example

A 1.5ct G VS2 round brilliant, lab-grown, IGI certified. High liquidity stone type: widely stocked, heavily searched, and frequently listed at multiple retailers simultaneously. Here's what the markup calculation looks like when six retailers hold the same certificate:

Retailer	Listed price	Deviation from cross-retailer median
Retailer A	$5,040	+20.0%
Retailer B	$4,620	+10.0%
Retailer C	$4,200	0.0%
Retailer D	$4,200	0.0%
Retailer E	$3,780	-10.0%
Retailer F	$3,570	-15.0%

Cross-retailer median: $4,200. Retailer A's observation for this stone is +20%. That observation joins every other matched stone observation we have for Retailer A this quarter. The end of quarter median across all those deviations becomes their leaderboard score.

The table uses illustrative prices to show the mechanics cleanly. The actual matched data for current quarters publishes in the Q2 2026 leaderboard update. But two things the example makes concrete regardless: the absolute dollar gap between Retailer A and Retailer F is $1,470 on the same stone. And the retailers sitting at the median aren't the cheapest. They're at the market midpoint. A buyer who finds one of them is paying competitive rates, not the floor.

One thing this calculation does not capture: service quality, warranty terms, return policies, ring setting quality, or anything else a retailer provides beyond the stone itself. The leaderboard is a diamond store comparison on stone price only. If a retailer charges a premium but includes a lifetime upgrade policy, gratis resizing, and a physical showroom where you can examine the stone before committing, that premium may be entirely rational. The leaderboard tells you what you're paying for the stone. The rest is your judgment.

What the rankings consistently show

Across every quarter we've run this index, a few structural patterns hold.

Natural round brilliants in the 0.7ct to 1.5ct weight range show the tightest retailer spread. This is the most competitive category in the market. High search volume, strong price transparency, and a buyer population that has learned to shop around. Retailers who overprice here lose sales quickly and most of them know it.

Lab-grown fancy shapes, particularly ovals and cushions, consistently show the widest variation. Lower search volume than rounds, less standardised pricing conventions, and greater cut quality variation that makes direct comparison harder for buyers. That combination creates pricing opacity that some retailers use and others don't.

A finding that matters practically: retailer ranking varies significantly by category. A retailer appearing expensive in the overall leaderboard can be genuinely competitive in lab-grown ovals specifically. One that ranks well on natural rounds can be expensive on natural fancy colours. The overall ranking is a starting filter, not a verdict. For any specific purchase, the category level figure is what actually matters. A targeted search on CaratHunter will show you the current price spread on the exact stone type you're considering, which is always more informative than a headline ranking.

Lab-grown rounds in popular weight ranges are showing the most dynamic pricing of any category in 2026. Prices have moved substantially year-on-year, and the retailer spread in this category has widened as some retailers pass decreases through quickly and others absorb them as margin. That divergence means the best diamond retailer price on a lab-grown round can shift materially between quarters.

Where the data has real limits

We track 110 retailers. We do not have equal confidence in all 110 rankings.

Smaller regional retailers with thin inventory contribute fewer matched observations. Their end of quarter deviation medians are less stable. We include them where the data permits and flag confidence levels explicitly. A ranking built on 40 matched observations is less reliable than one built on 4,000. Not marginal. The quarterly tables show the counts, and that number matters.

Regional pricing creates a currency normalisation challenge. Retailers priced in AUD, GBP, EUR, and CAD all appear in the index. We convert to USD using the prevailing exchange rate at the time of the price snapshot. Exchange rate movements can shift a retailer's apparent position between quarters even if their actual pricing strategy hasn't changed at all. Each quarterly release notes the exchange rate used.

There's a harder structural limit we're working on actively. Some retailers list stones at competitive prices on the product page, then apply service fees or checkout markups that push the final purchase price well above what the listing shows. The leaderboard currently reflects listed prices. It may therefore understate the effective cost at some retailers. We're building checkout price tracking to close this gap, and we'll restate historical rankings that would change materially once it's live.

Retailers with large exclusive inventory present a related issue. Stones with no external certificate match can't enter our comparison at all. For retailers where much of the inventory is exclusive to their own feed, the matched sample may not represent what they actually sell. We note this in coverage labels where it applies, but buyers should factor it in.

What's coming next

The Q2 2026 leaderboard update publishes the full ranked table for this quarter: category breakdowns, matched observation counts, and the complete list from most expensive to most affordable across all retailers meeting our minimum coverage threshold. That's where the actual retailer names and deviation scores are.

Two open questions for the next methodology revision. Whether to move to monthly snapshots for lab-grown categories, given how quickly intra-quarter prices are moving in 2026. Monthly would be more timely; quarterly is more stable. We haven't resolved it. And how to handle checkout price data once that tracking is operational. Both changes would affect some rankings, and we'll publish any methodology revision before implementing it.

The leaderboard isn't a judgement on any individual retailer. It's a record of what they charged for specific stones at specific times, relative to the same stones at other retailers. Some charge more and genuinely deliver more. Some don't. The data makes that distinction visible. Every number comes from a real listing, at a real retailer, on a real date. That standard doesn't change.