The Rapaport list gives an asking price per carat for each shape, size, colour and clarity, in hundreds of US dollars. Traders price a diamond as a discount from that list: “−35” or “35 back” means 35% below the list. Price per carat = list price × (1 − discount ÷ 100); the stone’s total = price per carat × carat weight.
What is the Rapaport price list?
The Rapaport Diamond Report is a price list for polished diamonds, published by Rapaport, with separate tables for round and for fancy (pear-based) shapes. Each table is split by size range, and each cell gives a price for one colour and clarity.
The figures are in hundreds of US dollars per carat: a cell showing 65 means $6,500 a carat. The list is a reference point the whole trade quotes from — actual deals are almost always done at a discount to it.
What does “−35% back” mean?
It means 35% below the Rapaport list price. Dealers say “35 back”, write “−35” or “−35%”, and all mean the same. A premium above the list — rare, for exceptional stones — is written as a plus: “+5” is 5% above.
The discount is how traders compare stones of different sizes and qualities on one scale: a deeper discount is a cheaper stone relative to the list.
How do you work out the price from Rap and a discount?
- Find the list price per carat for the stone’s shape, size, colour and clarity, and turn it into dollars (65 → $6,500).
- Apply the discount: price per carat = list × (1 − discount ÷ 100).
- Multiply by the weight: total = price per carat × carats.
Going the other way, if you know the price per carat you want: discount = (price per carat ÷ list price − 1) × 100.
A worked example
Say the list shows 70 for a stone’s cell (the figure here is made up — use the current list). That is $7,000 a carat. At 35 back the price per carat is $7,000 × 0.65 = $4,550. A 1.20 ct stone is then $4,550 × 1.20 = $5,460.
If a buyer offers $4,200 a carat instead, that is (4,200 ÷ 7,000 − 1) × 100 = −40, or 40 back.
Rap discount calculator
Use the current Rapaport list cell for the stone’s shape, size range, colour and clarity. The figures above are an example, not list prices.
Why does the same discount mean a very different price at another size?
Because the list jumps between size ranges. A 0.99 ct and a 1.00 ct stone of the same colour and clarity sit in different ranges, and the 1.00 ct range has a much higher list price per carat — so even at the same discount the 1.00 ct costs far more per carat. These “magic sizes” (0.50, 0.70, 0.90, 1.00, 1.50, 2.00 ct and so on) are why weight just over a line is worth so much.
This is also why a discount alone never prices a stone: you always need the right list cell first, for the right shape table, size range, colour and clarity.
How Avirat keeps Rap and discount
Avirat stores the Rap price and the discount on every diamond line of a purchase, memo or sale, alongside the rate and amount, and the margin report shows your average discount to Rap across what you sold. You type the list price you are working from; Avirat does not publish Rapaport’s list.
See how Avirat handles this: Diamond software · Free tool: Rap discount calculator