Five RAPI sizes sit below peaks set in late September
Every size on Rapaport's daily series is higher over the 30 days to 4 October. Every one is also below a peak set between 21 and 26 September, the 0.30-carat by 1.26%.
By Carat Capital
What changed
Every size is off its peak. Rapaport's daily series is higher on all five sizes over the 30 days to 4 October. All five now sit below a peak set in late September. The 0.30-carat is 1.26% under its own.
What it means
- If you quote the month figure: It is true and it is trailing, measured from a 4 September base near the bottom of the range.
- If you are marking stock this week: Direction since the third week of September is down on every size, by 0.23% to 1.26%.
- What this is not: A fall in the index. All five sizes remain above where they started.
Key figures
| Sizes below their window peakpeaks dated 21 to 26 September | 5 of 5 |
|---|---|
| 0.30-carat against its own peak$960.16 against $972.39 on 23 September | −1.26% |
| 1-carat against its own peak$3,911.50 against $3,920.47 on 25 September | −0.23% |
| 0.30-carat over the 30-day windowthe largest of the five, from a 4 September base | +2.89% |
Source: Rapaport Diamond Price Index, embedded daily series, window 4 September to 4 October 2026, 31 points per size · page read direct, 305,250 bytes, 4 October 2026
The month and the fortnight disagree
Both read alike. The 0.30-carat is up 2.89% over the window and 1.26% below its 23 September high of $972.39. The 1-carat is up 0.34% and 0.23% below its $3,920.47.
Base explains it. The window opens 4 September, near the bottom of its own range. A positive trailing column and a falling fortnight sit together without either being wrong.
| Size | 4 Sep | Peak | Peak date | 4 Oct | Vs peak | Page's own % |
|---|---|---|---|---|---|---|
| 0.30-carat | 933.19 | 972.39 | 23 Sep | 960.16 | −1.26% | 2.89 |
| 0.50-carat | 1,287.61 | 1,320.31 | 26 Sep | 1,315.42 | −0.37% | 2.16 |
| 1.00-carat | 3,898.25 | 3,920.47 | 25 Sep | 3,911.50 | −0.23% | 0.34 |
| 2.00-carat | 10,593.76 | 10,679.57 | 21 Sep | 10,647.79 | −0.30% | 0.51 |
| 3.00-carat | 17,900.21 | 18,211.68 | 21 Sep | 18,138.29 | −0.40% | 1.33 |
Notes on this table
The 4 September and 4 October columns are the first and last points of each size's embedded 31-point daily series, read out of the page's own JSON. The peak column is the highest point inside that same window and the peak date is its date; both are Carat Capital's reading of the series, not fields Rapaport prints. The Vs peak column is Carat Capital's division, newest over peak, less one: 960.16/972.39 = 98.74% of the peak, so 1.26% below it. The final column is the unlabelled percentage Rapaport prints beside each size; dividing last point by first reproduces it on 5 sizes out of 5, which establishes it as a trailing-window change. Levels on this page are restated after publication, reported by Carat Capital on 22 September 2026, so a quote needs the date the series was read as well as the date of the point: these were read on 4 October 2026.
The peaks cluster in one week
Five days apart. The 2-carat and 3-carat peaked on 21 September, the 0.30-carat on 23 September, the 1-carat on 25 September and the 0.50-carat on 26 September.
No new high. No size has set a window high in the eight days to 4 October. The gaps run from 0.23% on the 1-carat to 1.26% on the 0.30-carat.
The page's percentage is established
Division reproduces it. Dividing each size's last point by its first reproduces Rapaport's unlabelled percentage on five sizes out of five, to two decimals.
What to watch
- 6 OctRapaport's next daily point, which would need $972.39 on the 0.30-carat to set a new window high
- Early OctRapaport's September RAPI monthly commentary, overdue on the release calendar
The story so far
Go deeper
What would change this call
A new high on any size inside the next week. The gaps are 0.23% to 1.26%, small enough that one firm session on the 1-carat or 0.50-carat would close them. A monthly RAPI commentary giving a different window would also change which number this desk treats as the headline figure.
How the index and the peak are built
RAPI is built from asking prices on RapNet for round, D to H, IF to VS2 goods, published daily since August 2026 with a one-session lag. The page carries a 31-point daily series per size in embedded JSON, and an unlabelled percentage beside each size.
Method
The page was fetched direct at 305,250 bytes on 4 October 2026 and the embedded JSON parsed rather than read off the rendered chart. Every level printed here is a point in that JSON. The peak, the peak date and the Vs peak column are Carat Capital's own computation over the same 31 points and are labelled as such; Rapaport publishes no peak field. The page's own percentage was checked by dividing last point by first on each size and matched on five of five. The 2 October point now reads 3,912.28 on the 1-carat, where this paper read 3,912.48 on 3 October; that restatement is the behaviour already reported on 22 September and is not treated here as a new finding.