What the category development index is
The category development index (CDI) measures how much of a category's sales happen in one market against how much of the population lives there, indexed so that 100 is exactly proportional. NielsenIQ's CPG dictionary puts it as "the percentage of sales for a category in a given market versus the percentage of the US population in that market" (NielsenIQ). A bone-broth category that does 3.4% of its national dollars in Denver, a market holding 2.0% of US households, has a Denver CDI of 170.
Its sibling is the brand development index (BDI), which runs the identical arithmetic on one brand's sales instead of the category's (NielsenIQ). The two are only useful together. Alone, a CDI tells you where a category lives. Alone, a BDI tells you where you are big. Side by side, they tell you where you are missing.
How CDI and BDI are calculated
Both indices are a ratio of two shares, multiplied by 100. The Universal Marketing Dictionary states CDI as category sales per household in the group divided by category sales per household nationally (Universal Marketing Dictionary), which is the same number arrived at from the other side:
- CDI = (market's share of national category dollars / market's share of national households) x 100
- BDI = (market's share of national brand dollars / market's share of national households) x 100
An index of 100 means proportional. 170 means the category does 70% more business there than population alone would predict. 60 means the brand is running at 60% of its own national rate.
The denominator is a choice and it has to be stated. Households, population and ACV all give different answers, and a CDI computed on households compared against a BDI computed on population is not a comparison. Pick one, write it on the slide.
Five markets, two indices
Copper Kettle is a shelf-stable bone broth doing $19.2M against a $480M national category, a 4.0% national share. Here are five markets:
| Market | Share of US households | Share of category $ | CDI | Share of brand $ | BDI |
|---|---|---|---|---|---|
| Denver | 2.0% | 3.4% | 170 | 1.2% | 60 |
| Portland | 1.9% | 3.0% | 158 | 3.9% | 205 |
| Dallas | 4.0% | 3.2% | 80 | 3.0% | 75 |
| Atlanta | 3.1% | 2.4% | 77 | 4.3% | 139 |
| Chicago | 3.4% | 3.4% | 100 | 3.4% | 100 |
Indices are unitless, which makes them easy to nod at and hard to act on. Turn them back into dollars and the meeting changes:
| Market | Category $ | Brand $ | Brand share of category | Vs. 4.0% national |
|---|---|---|---|---|
| Denver | $16.32M | $230,400 | 1.41% | -2.59 pts |
| Portland | $14.40M | $748,800 | 5.20% | +1.20 pts |
| Dallas | $15.36M | $576,000 | 3.75% | -0.25 pts |
| Atlanta | $11.52M | $825,600 | 7.17% | +3.17 pts |
| Chicago | $16.32M | $652,800 | 4.00% | par |
Denver is the finding. It is tied with Chicago for the largest category pool of the five at $16.32M, the category over-develops there by 70%, and Copper Kettle holds 1.41% of it. Getting Denver to the brand's own national share would be $652,800 instead of $230,400, a gap of $422,400 in one market with no new product and no new category demand required. Portland, where the brand feels successful, has a smaller pool and the brand already over-indexes at BDI 205.
The four-quadrant read
Cross the two indices at 100 and you get the read that makes the pair worth computing.
| High CDI (over 100) | Low CDI (under 100) | |
|---|---|---|
| High BDI (over 100) | Defend. Category and brand both strong. Portland. | You are the category here. Growth needs the category to grow. Atlanta. |
| Low BDI (under 100) | The opportunity. The demand is in this market and you are not. Denver. | Deprioritize. Neither the category nor the brand is developed. Dallas. |
The high-CDI / low-BDI corner is the one worth the budget, and it is the one a national share number hides completely. Copper Kettle's 4.0% national share looks the same whether Denver is at 1.41% or 6%, and the whole difference is whether the brand has a distribution problem in the market where shoppers most want the category.
The mirror corner deserves a warning. Atlanta at CDI 77 and BDI 139 feels great and is fragile: the brand holds 7.17% of a category pool 23% smaller than its population would suggest, so it is a big fish in a small pond, and the growth ceiling is set by the category rather than by the brand.
What the indices hide
- A low BDI is not automatically a demand problem. Check ACV-weighted distribution in the market first. A BDI of 60 on 22% ACV is a distribution gap; a BDI of 60 on 78% ACV is a velocity problem, and the two get opposite budgets.
- Markets are not metro areas. A syndicated "market" is a defined geography with a fixed store list, and its boundaries rarely match the ones a sales team uses. Compare index to index inside one provider's market definition, never across two.
- Small markets swing. A market with 0.4% of households can post a BDI of 240 off a handful of doors. Set a minimum dollar or store floor before an index earns a decision.
- An index says where, never who. CDI and BDI are sales divided by a population count. They support a geographic read and they cannot support a claim about shopper age, income or attitude. Those need loyalty-linked demographics or a survey.
Where Scout fits
Scout reads POS and syndicated data by geography, so CDI and BDI by market, against the household or population denominator you specify, are a query rather than a quarterly spreadsheet rebuild. It will also hold the dollar translation next to the index, which is the version people act on. What it does not do is observe shoppers: no visit, catchment or footfall panel sits behind these numbers, and the indices describe transactions rather than the people making them.
The short version
- The category development index (CDI) indexes a market's share of category dollars against its share of households. 100 is proportional, over 100 is over-developed.
- The brand development index (BDI) runs the same math on one brand. Neither is useful alone.
- High CDI with low BDI is the opportunity quadrant: the demand is in that market and the brand is not. Denver at CDI 170 / BDI 60 was worth $422,400.
- Before acting on a low BDI, check distribution in that market. Half of what looks like weak demand is missing doors.