RAPI's 0.30-carat gains 3.2% in September, the 1-carat 0.3%
Rapaport's monthly release again puts small round goods ahead of large ones. The 3-carat index turned positive after August's 0.4% decline, and the year-to-date column reads 15.1% on the smallest of the four sizes.
By The Diamonds Desk
What changed
The 3-carat turned. Rapaport's September release has the 3-carat index up 1.5% after August's 0.4% fall. The 1-carat rose 0.3%, its second consecutive monthly increase.
What it means
- If you hold small round goods: The 0.30-carat has done the year's work at 15.1% and carries the most to give back.
- If you price 1-carat stones: 0.3% is a second rise, not a recovery. The size has been the flattest of the four all year.
- If you sell at the bottom of the range: Rapaport reports smaller, lower-quality goods still under lab-grown pressure. The index gain does not reach you.
- What this is not: A report of settled trades. RAPI measures asking prices on one marketplace.
Key figures
| 0.30-carat, Septemberlargest of four sizes | +3.2% |
|---|---|
| 0.50-carat, Septembermatches August | +2.5% |
| 1-carat, Septembersecond rise running | +0.3% |
| 3-carat, Septemberreverses August's fall | +1.5% |
Source: Rapaport Trade Diamond Index · monthly release, New York, 6 October 2026 · asking prices, round D-H IF-VS2
The small end leads again
Ten times the move. The 0.30-carat's 3.2% is 10.7 times the 1-carat's 0.3%, on Carat Capital's division of the two figures.
Rounds beat fancies. Rapaport attributes the gap to round production having fallen more sharply than fancy-shape production in earlier months.
| Size | September | August | Year to date |
|---|---|---|---|
| 0.30-carat | +3.2% | +2.0% | +15.1% |
| 0.50-carat | +2.5% | +2.5% | +5.8% |
| 1-carat | +0.3% | +0.5% | not given |
| 3-carat | +1.5% | −0.4% | not given |
Notes on this table
September figures are from Rapaport's release of 6 October 2026, read from the page's own body paragraphs. August figures are the ones Rapaport published on 2 September 2026 and Carat Capital printed on 3 September; they are looked up in that article, never re-derived. Year-to-date figures are published for two sizes only and the other two cells say so rather than carry an estimate. Rapaport's release gives no year-to-date figure for the 1-carat or 3-carat.
The 3-carat reverses August
A one-month decline. August's release had the 3-carat down 0.4% after what it called a year and a half without a move. September puts it up 1.5%.
Second half carried it. Rapaport says most of the 3-carat's advance came in the month's second half rather than across the whole period.
The price list moved mid-month
A dated increase. On 11 September Rapaport raised its price list for certain round 0.30 to 0.69-carat, D-G, VVS1-SI1 diamonds.
Two instruments. The index measures asking prices on Rapaport Trade. The list is Rapaport's own published benchmark and moves by decision, not by averaging.
Lab-grown still holds the bottom
The cheap end lags. Rapaport reports smaller, lower-quality diamonds stayed under pressure from lab-grown competition through the month.
The reference is flat. Carat Capital's tape carries the one-carat lab-grown reference at $651, unchanged on the prior session.
What to watch
- Early November 2026Rapaport's October release. Tests whether the 3-carat holds its reversal and whether the 1-carat posts a third consecutive rise.
- Through October 2026Rapaport Price List revisions. September's came on the 11th; a second increase would move the published benchmark, not only asking prices.
- 9 November 2026Phillips' Geneva Jewels Auction: VII prices large polished at the top of the market, against an index that measures the cheapest tenth of listings.
The story so far
Go deeper
What would change this call
A negative month in the small sizes. The 0.30-carat carries 15.1% of year-to-date gain and the most to give back; a fall there would end the pattern Rapaport has reported since July.
How RAPI is built
Rapaport defines RAPI as the average asking price of the 10% lowest-priced round diamonds in each of the top 25 quality categories — D-H, IF-VS2, GIA-graded, RapSpec-A3 and better — offered for sale on Rapaport Trade, the marketplace formerly called RapNet. It is an index of what sellers ask, not of what buyers paid, and it reads the cheap tenth of each category rather than the middle.
Method
The release was fetched to raw bytes at rapaport.com, HTTP 200, 460,898 bytes, saved to newsroom/sources/2026-10-06/rapi-sept.html. Figures were greped only inside the story's own body paragraphs, stopping before the page's More Stories widget, because a whole-page grep on this site also matches figures belonging to adjacent stories. Exact-digit greps on the saved file: 3.2% one hit, 2.5% one, 0.3% one, 1.5% one, 15.1% one, 5.8% one, September 11 one. The release's own dateline reads New York, NY – October 6, 2026 and the feed stamps it Tue, 06 Oct 2026 08:41:35 +0000. Archive check, by entity and period, not by figure: Carat Capital's own monthly-release coverage is a-half-a-percent-after-fifteen-months.html, which covers the AUGUST 2026 release (1-carat +0.5%, 0.30-carat +2%, 0.50-carat +2.5%, 3-carat −0.4%); this item covers the SEPTEMBER 2026 release. Different reporting period, same entity, so advanced, not a repeat. The paper's 30 September, 3 October and 4 October pieces read Rapaport's separate DAILY series on 30-day trailing windows and are a different instrument with different figures; they are named here so the two are not confused. The one quote carried below was counted at 11 words before it was written.