Diamond prices in September 2026: natural climbs while lab-grown keeps falling

The September 2026 Caratlytics Diamond Price Index puts the natural median at USD 2,334.70 per carat, up 7.52% from August, while lab-grown fell to USD 443.12 per carat, down 4.77% over the same period. The natural to lab ratio now sits at 5.3 to 1, up from 4.7 to 1 in August, a natural premium of 426.9%. These two markets are not converging. They're pulling apart.

The overall median across both categories sits at USD 809.09 per carat, up 5.2% from USD 769.08 in August. That blended figure reflects the relative weight of lab-grown listings: 2,183,916 lab-grown observations versus 1,270,622 natural in this month's systematic sample, drawn from 144 active retailers.

What moved by shape

Natural diamonds had a strong month across most cuts. Pear shapes led at 13.7%, finishing at USD 2,306.88 per carat. Radiant cuts were close behind at 13.2%, landing at USD 3,091.09 per carat, the highest-priced natural shape in this month's index. Marquise added 10.8% and oval gained 10.2%.

Asscher was the only natural shape to fall, dropping 3.3% to USD 2,503.52 per carat. Cushion barely moved, up just 1.7%.

Lab-grown moved opposite almost everywhere. Emerald cuts fell 8.3% to USD 451.21 per carat. Ovals dropped 7.4% to USD 453.36 per carat. Pear, round, and princess all fell between 4.8% and 5.1%. The one exception was cushion, which gained 6.9% to USD 516.05 per carat, making it the most expensive lab-grown shape this month.

Shape	Natural (USD/ct)	Natural MoM	Lab-grown (USD/ct)	Lab MoM
Radiant	3,091.09	+13.2%	473.93	-2.1%
Cushion	2,947.51	+1.7%	516.05	+6.9%
Oval	2,654.67	+10.2%	453.36	-7.4%
Asscher	2,503.52	-3.3%	470.45	-4.3%
Heart	2,374.19	+9.8%	421.49	-1.8%
Pear	2,306.88	+13.7%	452.34	-5.1%
Emerald	2,278.03	+6.2%	451.21	-8.3%
Marquise	2,268.14	+10.8%	484.70	-3.2%
Round	2,248.06	+7.6%	413.85	-5.0%
Princess	2,158.00	+5.7%	461.36	-4.8%

Round at USD 2,248.06 per carat and princess at USD 2,158.00 per carat are the two cheapest natural shapes. The gap between round and radiant sits at USD 843 per carat this month, wider than a typical spread between the two most popular natural cuts.

The certificate premium

The gap between GIA and IGI lab-grown pricing is now too large to attribute to quality alone. GIA-certified lab-grown diamonds came in at USD 973.00 per carat this month. GCAL sat close at USD 979.17 per carat. IGI, which certifies most lab-grown volume, came in at USD 424.24 per carat. That's a difference of over 129%.

Some of that gap reflects genuine quality variation in what each lab certifies. IGI handles greater volume across a wider quality spread. But buyers paying GIA lab-grown prices are also paying for market perception, and it's worth being clear-eyed about what that premium actually buys in practical terms.

For natural diamonds, EGL-certified stones averaged USD 3,216.00 per carat, well above the rest. EGL grading is widely considered less rigorous than GIA, which means these stones are likely carrying prices that GIA-equivalent grading wouldn't support. HRD naturals averaged USD 2,758.39 per carat, above GIA's USD 2,379.08. IGI naturals at USD 1,758.76 per carat sit significantly lower, reflecting both the average quality distribution in IGI-certified natural stock and the market's strong preference for GIA on the natural side.

Certificate	Natural (USD/ct)	Lab-grown (USD/ct)
EGL	3,216.00	n/a
HRD	2,758.39	645.52
GIA	2,379.08	973.00
GCAL	n/a	979.17
IGI	1,758.76	424.24

The cross-retailer spread

Over 4.9 million diamonds in our index are listed at more than one retailer. The cross-retailer spread data is one of the sharpest tools we have for identifying where buyers are being overcharged.

For natural diamonds, 1,507,445 multi-retailer stones showed a median spread of 75.6% and an average of 90.1%. A 75.6% median spread means a typical certified natural diamond is available somewhere for 75.6% more than the cheapest listing for the same stone. The aggregate dollar spread across all natural multi-retailer diamonds totalled USD 3,758,399,153.

Lab-grown is a different order of magnitude. The 1,422,841 multi-retailer lab-grown stones show an average spread of 207.2% and a median of 218.9%. The median sitting above the average points to a concentration of very wide spreads in the middle of the price distribution, rather than a handful of extreme outliers skewing the figure upward. For a buyer near the top of that spread, an identical stone with the same certification is often available at less than a third of the price elsewhere. The aggregate spread across lab-grown multi-retailer diamonds was USD 2,277,652,612.

Segment	Multi-retailer diamonds	Avg spread	Median spread
Natural	1,507,445	90.1%	75.6%
Lab-grown	1,422,841	207.2%	218.9%

Reading the numbers as a buyer

The 2ct range absorbed the largest absolute dollar impact from September's natural gains. Pear and radiant each cleared 13% in a single month, so buyers with flexibility on shape are better positioned right now than those committed to a specific cut. If you've been watching radiant naturals in particular, September moved materially against you.

Asscher naturals softened 3.3%. It's the one area where September moved in a buyer's favour on the natural side. If you've been watching asscher cuts, this was a better month to buy than August.

For lab-grown, everything except cushion fell. The emerald cut drop of 8.3% is meaningful at higher carat weights where the per-carat saving compounds. Oval fell 7.4%, and most other shapes dropped 3% to 5%.

The cert decision matters more in lab-grown than in natural, given the 129% spread between IGI and GIA pricing. Paying nearly USD 549 more per carat for a GIA lab-grown over an IGI stone is a decision worth making deliberately. The resale premium for GIA over IGI in lab-grown is unlikely to be anywhere close to that gap.

Our diamond price index tracker carries both natural and lab-grown medians by shape, which makes it straightforward to check whether a specific listing sits above or below the current market median.

What we're watching in October

The natural to lab ratio at 5.3 to 1 is the number to follow. A continued natural rally alongside continued lab-grown softening would push that ratio toward 6 to 1. At that level, the price difference between the two categories is so large that the buying decision becomes almost entirely about preference rather than relative value.

Lab-grown cushion broke from the downward trend with a 6.9% gain. Whether that represents genuine demand concentration in cushion cuts or a one-month anomaly will be clear in the October release.

The cross-retailer median spread for lab-grown at 218.9% hasn't been improving. That's still the most actionable figure in the entire index for most buyers. Comparison shopping captures far more savings than timing the monthly index move. The October release will tell us whether September's 7.52% natural gain had real momentum behind it, or was a single month's correction. The baseline is USD 2,334.70 per carat.