The BPI is calculated by combining three subindices—each determining the basic criteria for investment in the biofortified crops—using a geometric mean.

Most of the country-level crop production and consumption data used are from the Food and Agriculture Organization of the United Nations (FAO); most of the data on country-level iron, zinc, and vitamin A deficiency are from the World Health Organization (WHO). The combined number is then rescaled into a crop- and micronutrient-specific score that indicates whether a country could benefit from a biofortification intervention. A country with a BPI score of zero is a "no-go" for a biofortification intervention, and a country with a score of 100 is the highest priority.

Crop scores are further divided into priority quintiles, with five distinct groups that range from the top 20 percent to the lowest 20 percent: Top, High, Medium, Low, Little, No. Top priority countries indicate the greatest potential for the biofortified crop to have a significant nutrition impact in the country; High priority countries indicate great potential for impact; Medium priority indicates fair potential for the biofortified crop; Low priority indicates some potential; while Little priority indicates the least potential for impact for that biofortified crop. An additional “No priority” category exists, which indicates zero potential for the biofortified crop in that country.

The crop scores are also ranked in descending priority order, from highest to lowest, such that the country with the highest BPI score (indicating top priority) receives a rank of 1 (indicating its suitability for biofortification investment).

Large countries may offer better opportunities for biofortification compared to smaller ones. We calculate two alternative indices which weigh each country according to their land area and size of the target population in relation to other countries.

While the BPI is useful in making investment decisions for biofortification, it should not be relied on in isolation. As calculated, the BPI does not explicitly take cost-effectiveness into account, nor does it allow for sub-national analyses. Disaggregated subnational analyses for larger countries have been carried out in several large countries to capture the heterogeneity in production, consumption, and micronutrient deficiency that may exist at a subnational level. Interactive results from these analyses will be available on this site in the future.