The 30% That Tells You Whether a Diamond Is Fairly Priced

The single biggest factor in a Caratlytics grade is whether the diamond's price is fair. Value carries 30% of the total score, more weight than any other component. Not the certificate. Not the cut. Price.

If you want the full picture of how all five components fit together, our guide to the Caratlytics methodology covers everything from Quality to Certification to how the final grade is calculated. This post stays narrow: how the Value subscore works, what it measures, and why two diamonds with identical specs can end up with completely different grades.

Every diamond lands in a bucket

Asking whether $6,000 is a "good price" for a diamond is like asking whether 15 minutes is a "good time" for a race. It depends entirely on context. A 1ct D IF round at $6,000 would be a steal. A 1ct J SI2 round at the same price would be absurd.

So we bucket. Every certified diamond in the index gets placed into a comparison group based on four dimensions:

Dimension	Grouping method	Why it matters
Shape	Exact match	Rounds, ovals, cushions each have distinct price curves
Carat weight	Narrow bands (1.00 to 1.09, 1.10 to 1.19, etc.)	Prevents a 1.01ct from being compared to a 1.48ct
Colour	Single grade	Each step in colour shifts market value measurably
Clarity	Single grade	Same principle; each grade is its own price tier

Within a bucket, every diamond shares the same shape, approximate weight, colour, and clarity. The variable that remains is price. Cut quality also varies, but that's scored separately in the Quality component.

Some buckets are massive. A popular combination like 1.00 to 1.09ct G VS2 rounds can hold tens of thousands of stones across our 110+ retailers. Others are genuinely tiny. A 3ct+ D IF marquise might contain fewer than ten listings in the entire index. Both situations need handling, which we'll get to.

Why medians beat averages

Once stones are bucketed, we calculate the median price for each group. Not the mean. This is deliberate.

Diamond pricing has a long right tail. Most stones in a given bucket cluster around a competitive market price, but there are always outliers on the expensive end. Retailers charging significant premiums for branding, bespoke service, or exclusive settings can list a stone at two or three times what the rest of the market asks. These aren't errors. They're real prices that real retailers charge.

A mean gets dragged upward by every one of those outliers. Stick five overpriced stones in a bucket of 100 and the average shifts noticeably. The median just sits at the price of the 50th stone, completely indifferent to extremes. If the top five listings are priced at double or triple the going rate, the median doesn't move.

This is why the median diamond price is a better reference point for buyers. It reflects what a reasonable, comparison shopping buyer should expect to pay, not what the most expensive option in the market costs. When we talk about a fair price diamond, we mean one that sits at or below this median within its bucket.

When buckets run thin

Not every bucket holds enough stones for a stable median. Unusual shapes at high carat weights in rare colour and clarity pairings might appear only a handful of times across the entire index. Calculating a diamond price percentile from three stones isn't meaningful.

When a bucket falls below our minimum size threshold, we widen the net. The carat band expands first: a 2.52ct stone gets grouped with the broader 2.50 to 2.99 range instead of the tighter 2.50 to 2.59 window. If that still isn't enough, we can relax one additional dimension.

Precision trades off against reliability here. A stone compared to a broader peer group gets a slightly less specific percentile. But a percentile drawn from 200 genuinely comparable stones is always more useful than one drawn from three. We'd rather be approximately right than precisely wrong.

The cross-retailer signal

The bucket percentile is the primary driver of the Value subscore. But there's a secondary signal: cross-retailer pricing.

Plenty of stones in the index are listed by more than one retailer simultaneously. Same physical diamond, same certification, different price tags. When we spot a stone priced below its own duplicates at other retailers, that adds a layer of confirmation. The bucket tells you the stone is well priced relative to the broader market. The cross-retailer comparison tells you it's well priced relative to itself.

Both signals pointing in the same direction earns a bonus on the Value subscore. A stone that sits in the lower half of its bucket and is also the cheapest listing of that particular certificate is doing double duty on the value front.

Not every stone has twins. Retailer exclusives or particularly unusual diamonds may appear only once in the index. In those cases, the subscore relies entirely on the bucket percentile. No penalty for having no duplicates; just no opportunity for the bonus.

Same specs, completely different scores

Two round brilliant diamonds. Both G colour, VS2 clarity, both sitting in the 1.50 to 1.59ct bucket. Same peer group. Same median reference.

Attribute	Stone A	Stone B
Shape	Round	Round
Carat	1.52	1.54
Colour	G	G
Clarity	VS2	VS2
Price vs bucket median	Below	Above
Value percentile	90th	30th
Cross-retailer twins	Cheapest listing	Midrange listing
Value bonus	Yes	No

Stone A is priced below the bucket median. Its diamond value score places it at the 90th percentile, meaning only 10% of stones in the same bucket are cheaper. That same certificate also appears at two other retailers, both asking more. The cross-retailer signal confirms the value and triggers the bonus.

Stone B is priced above the median. It lands at the 30th percentile: 70% of comparable stones offer better value. The certificate appears at one other retailer at a similar price. No bonus.

Same 4Cs. Same bucket. Entirely different Value subscores. One lifts the overall Caratlytics grade; the other pulls it down. The specs tell you what the diamond is. The Value subscore tells you whether you're paying a fair price for it.

What the heaviest weight does to a grade

At 30%, Value outweighs both Quality and Certification as individual components. For most buyers, price-to-quality is the core question, and the weighting reflects that.

Across our index of 8,708,893 scored stones, the overall Caratlytics grade distribution looks like this:

Grade band	Stones	Share of index
A+ (90 to 100)	32,263	0.4%
A (80 to 89)	3,253,800	37.4%
B (70 to 79)	2,299,009	26.4%
C (60 to 69)	1,952,430	22.4%
D (below 60)	1,171,391	13.5%

Only 0.4% earn the top grade. Value is often the subscore that determines whether a diamond with strong quality and a reputable certificate lands in A or B territory. Overpriced stones with excellent specs still get pulled down.

Natural diamonds average a 71.9 Caratlytics score across the index. Lab-grown stones average 74.2. That small gap is driven largely by Value: lab-grown pricing tends to be more compressed, with fewer extreme outliers priced well above the median, so stones cluster tighter around the centre of each bucket and score more consistently.

We're continuing to refine how the fallback logic handles small buckets, testing whether relaxing clarity before carat gives more accurate comparisons in thin categories. As we add retailers to the index, bucket sizes grow, medians stabilise, and the percentiles get sharper. The Value subscore is a living calculation, recalculated as the market moves.

For how the other components work alongside Value, the Quality score breakdown and Certification score breakdown cover the next two weightings in detail.