The carat cliff
Diamond prices do not rise smoothly with weight — they step, hard, at the weights people ask for by name. We measured every step, and the one at a carat is large enough to buy two color grades and leave change.
Diamond prices do not rise smoothly with weight. They step, sharply, at the round numbers — and the step is big enough that a 0.99 carat E color costs less than a 1.00 carat G, is two color grades better, and faces up about two hundredths of a millimeter smaller.
That is not a rounding artifact or a quirk of one retailer. It happens at every magic weight, and the largest step of all is at half a carat, where crossing the line costs 44%.
Why the steps exist
Diamonds are priced per carat, and the price per carat itself jumps at weights people ask for by name. Nobody walks into a shop asking for a 0.94. They ask for a half carat, or a one carat, so that is where demand concentrates and where the per-carat rate resets upward.
A cutter faces the same incentive from the other side. Given rough that could yield a beautifully proportioned 0.96 or a slightly deep 1.01, the 1.01 is worth materially more, so that is frequently what gets cut — which is also why stones just over a round number are sometimes cut a little deep, hiding weight in the pavilion where it does not show.
The result is a market where the hundredth of a carat either side of a round number is the most expensive hundredth you will ever buy.
Every cliff, measured
Mid-point retail for a well-cut round brilliant at G color and VS2 clarity, one hundredth under each magic weight against the weight itself. Face-up diameter from the cube-root relationship between weight and width.
The half-carat step is the steepest in proportional terms and the one that matters most to the people least able to absorb it. At the top end the percentages settle around a third, but a third of a large number is a lot of money.
What stepping back buys you
At the one carat line, the saving from dropping to 0.99 compared against what the same money buys in color on the smaller stone.
This is the part worth sitting with. The saving does not just cover an upgrade — it overshoots it. You can move two color grades, from G to E, and still be $275 better off than the 1.00 carat G you were originally looking at. The stones are visually the same size. One has noticeably better color and a smaller number on the certificate.
The saving by color grade
What you keep by buying 0.99 instead of 1.00, at each color grade. The better the stone, the more the hundredth of a carat costs.
When not to do this
Two honest caveats, because the strategy is not free.
If the number matters to you, the number matters. Some people want a certificate that says one carat, and there is nothing irrational about that — it is the thing being bought. This analysis prices the trade-off; it does not tell you the trade-off is wrong.
Resale inherits the same cliff. A 0.99 is harder to sell than a 1.00 for exactly the reason it was cheaper, so the discount you enjoyed going in is a discount you concede coming out. Since diamonds resell at 25–40% of retail regardless, this matters less than it sounds — but it is not nothing, and anyone presenting the just-under stone as free money is not being straight with you.
It also stacks with the other direction-reversing grade on a certificate: see where a diamond’s fluorescence stops being a fault.
How this was calculated
Same basis as everything else here, and the same caveat. This is a modeled analysis, not a dataset of transactions. The per-carat curve, the color and clarity multipliers and the bracket boundaries are our own pricing model, published in full on the price index and explained on the methodology page.
Face-up diameter is computed from the cube-root relationship between weight and linear dimension, which is why the difference across a cliff is around two hundredths of a millimeter rather than zero. Our size charts round to one decimal place and would show the two stones as identical; they are not quite, and the honest figure is the one above.
Figures are indicative retail for a well-cut natural stone and will not match any individual quote. Real cliffs are a little softer than modeled ones, because a 0.995 exists and gets rounded on the certificate.
Use this
Published under Creative Commons Attribution 4.0. Reproduce the tables, chart them, quote the numbers — commercially included — provided you credit CaratBase and link back.
CaratBase. The Carat Cliff: what a hundredth of a carat costs. Retrieved , from https://caratbase.com/carat-cliff-study.html
To price your own weight against the cliff either side of it, use the price per carat chart or the valuation tool.