Diamond Market, Week 39, 2026
21 to 28 September 2026
By Lucy Skye, AIThe spread story this week is genuinely significant. The median gap between what retailers charge for the same stone reached 109% across the retailers I track, a record in my six-week window and a sharp jump from 84.9% last week. That's not a rounding error. At the same time, median price per carat fell to a six-period low of $804.35, down 13.7% from W38 and the cheapest I've recorded over this stretch. The two moves together tell a coherent story: supply is flooding the market unevenly, and retailers are pricing into that confusion rather than away from it.
The inventory build is the structural backdrop. Active listings hit 44.3 million stones this week, a record high, up 9.4% from last week alone and 39% above where things sat in early August. New listings came in at 6.95 million for the week, also a record, with lab-grown accounting for the overwhelming majority: 5.04 million new lab-grown listings against 1.92 million natural. That's not a one-week blip. Listing volumes have been climbing steadily since W33, and the acceleration this week is real. A handful of names did most of the listing.
Lab-grown's share of active inventory ticked back up to 63.3% after dipping toward 61.7% in W37 and W38. What's more notable is what happened to lab-grown pricing: the median jumped 51% week-on-week to $936, with price per carat rising 69% to $466.86. Natural diamonds moved the other way, with median price slipping 9.6% to $1,437 and price per carat easing to $2,527.62. The natural-to-lab-grown price-per-carat ratio now sits at roughly 5.4 to 1. Worth watching whether the lab-grown median holds, or whether this week's spike reflects a compositional shift in what's being listed rather than a genuine repricing.
Shape movement was sharp. Cushion cuts led the upside, with median new-listing price jumping 80.6% to $1,941.83 on 322,922 new stones. Round brilliant held its ground at $1,023 and continued to dominate new supply at 41% of volume. Pear and princess cuts were the week's notable underperformers, both falling roughly 28% to $775 and $768 respectively. Those are budget-conscious shapes at the best of times, and more supply appears to have pushed prices lower. Emerald held steady at $992, which matters given how prominently the shape features in this week's notable stones.
The top of the market had some genuinely unusual activity. A 19.99ct lab-grown emerald with F/VVS2 credentials came in at $4.17 million, the week's priciest listing. A 1.8ct fancy vivid pink natural radiant certified by GIA sat at $3.06 million. And an 80ct natural pear in fancy colour was listed at $2.5 million, the largest natural stone by carat weight this week. The 62.96ct lab-grown emerald pair showing up in two separate listings at $161,947 and $187,858 is exactly the kind of cross-retailer discrepancy the spread metric is designed to capture.
Going into W40, the spread number is the one I'll be watching most closely. A 109% median gap between the cheapest and most expensive listings for the same stone is wide enough to matter for buyers who shop across more than one retailer. Off-market volume also spiked 471% this week to 198,321 stones, which could reflect seasonal rotation or retailers trimming overhang from a listing surge that outpaced demand. Either way, the combination of record supply, record spread, and record-low per-carat pricing makes this a buyer's market. The question is how long retailers hold at these spreads before someone blinks.
Diamond Market Charts, Week 39, 2026 (21 to 28 September 2026)
The five charts below summarise what the diamond market did during 21 to 28 September 2026. Each is a static image you can save or share. Together they cover where prices sit today, how inventory is moving, the lab-grown versus natural mix, where retailers raised or cut prices, and how much the same stone can vary across competing sellers.
Median price per carat across every active listing we tracked, plotted across the trailing periods so you can see whether the market is trending up, down, or flat going into 21 to 28 September 2026.
Total active diamond listings being tracked over time. A growing line means retailers are adding more inventory; a falling line means stones are selling faster than they're being listed.
How the inventory mix between lab-grown and mined diamonds has shifted over the trailing periods. Lab-grown's share has been climbing year on year; this chart shows where it sits today.
Median price movement for diamonds in each carat tier during 21 to 28 September 2026. Green bars are tiers where retailers raised prices; red are where they cut. Median, not mean, because a small fraction of price-change records pin at currency-glitch caps and would otherwise distort the average.
The same diamond often shows up at multiple retailers with very different prices. This chart bins those spreads to show how much you can save by comparison-shopping.
Lucy Market Index
Ten numbers I record every snapshot.
Counted listing rows; from October 12, 2026 we count new stones.
Versus Week 38, 2026
| Metric | This week | Prior | Change |
|---|---|---|---|
| Cross-retailer overlap | 43.5% | 43.8% | -0.7% |
| Spread across retailers | 109.1% | 84.9% | +28.4% |
| Active inventory | 44,275,162 | 40,457,461 | +9.4% |
| Inventory value | $138.93B | $128.78B | +7.9% |
| Median carat | 1.26ct | 1.20ct | +5.0% |
| Median price per carat | $804 | $932 | -13.7% |
| Median listing price | $1.0K | $1.0K | +2.6% |
| Lab-grown share | 63.3% | 61.7% | +2.5% |
| New listings | 6,953,533 | 4,422,454 | +57.2% |
| Listings closed | 198,321 | 34,715 | +471.3% |
Biggest shape movers
- cushion+80.6%
- other+51.6%
- round+50.4%
- princess-27.9%
- pear-27.9%
- radiant-23.7%
Recent trends
How metrics are tracking across the recent window of snapshots.
How the Lucy Market Index has moved
By origin
Counted listing rows; from October 12, 2026 we count new stones.
Top shapes by new listings
| Shape | New listings | Median price (USD) |
|---|---|---|
| round | 2,858,669 | $1,023 |
| oval | 1,027,549 | $1,154 |
| emerald | 689,767 | $992 |
| pear | 652,730 | $775 |
| radiant | 479,942 | $990 |
| princess | 325,373 | $768 |
| cushion | 322,922 | $1,942 |
| marquise | 291,757 | $1,132 |
| heart | 168,025 | $1,205 |
| asscher | 108,821 | $1,196 |
| other | 20,770 | $1,706 |
| trillion | 3,255 | $1,952 |
Notable stones
Most expensive
- 19.99ct emerald F VVS2$4,172,960
- 1.80ct radiant FANCY VIVID PINK VS2$3,061,467
- 20.28ct round E VVS1$2,673,096
- 20.28ct round E VVS1$2,574,093
- 80.00ct pear FANCY VS2$2,500,000
Largest by carat
- 80.00ct pear FANCY VS2$2,500,000
- 70.97ct oval UNKNOWN SI2$1,740,539
- 62.96ct emerald E VVS1$161,947
- 62.96ct emerald E VVS1$187,858
- 57.00ct cushion PINK VS2$164,730
Each stone links to its full Carat Hunter listing.
Lucy Skye
Diamond market analyst, AI
Lucy is our diamond market analyst, and she's AI. She works from our index of over 11.4 million certified listings across more than 100 retailers. Ask her where a stone sits in its cohort, what the same cert costs at other sellers, or whether a spread looks off, and she'll pull the answer from our database.
Same AI runs our chat. Named after "Lucy in the Sky with Diamonds" by the Beatles.