Learn / Price findings
Three City Areas Drove Half of September's Burger Index Rise
September's Burger Index averaged 14 cents above August across 12 city areas. Three areas drove half the rise, largely through hamburger buns.
Burger Index, CostInflation’s fixed-serving grocery basket for one double-patty burger, averaged $5.31 across 12 tracked city areas in September, up about 14 cents from August’s $5.17. East St. Louis, Jackson and Clayton accounted for just over half of that 12-area increase.
Every area’s monthly average rose, but the three largest gains were 24 to 35 cents. The other nine areas averaged a nine-cent rise. One bun supplied most of the difference between those groups.
The Burger Cost by City combines fixed servings of beef, a bun, American cheese, produce, pickles and condiments. This comparison averages each area’s daily basket values for all 31 days of August and all 30 days of September, then gives each of the 12 areas equal weight.
Three areas moved much more than the rest
East St. Louis gained 34.5 cents, Jackson 26.5 cents and Clayton 24.4 cents on a September-versus-August monthly-average basis. Their combined group averaged a 28.4-cent rise. Across the other nine areas, the mean gain was about nine cents, from 4.1 cents in Seattle to 14.2 cents in Jacksonville.
Those three larger moves supplied 51% of the 12-area average increase, despite representing only a quarter of the areas. This was a broader rise than a single outlier, but the magnitude was concentrated.
Buns explain most of the separation
The hamburger bun price index is measured for a 10-bun equivalent; the burger basket uses one-tenth of that value for one bun. That weighted component added 25.6 cents to the three-area monthly mean, versus 3.2 cents across the other nine areas.
Across all 12 areas, buns accounted for 8.8 cents of the 13.8-cent basket increase, about 64%. Lettuce added another 2.8 cents. The remaining ingredients together added about 2.2 cents.
These are changes in indexed basket costs. The index reflects both observed prices and which products are present on each date. The live Burger Cost by City and bun history show whether the three-area separation persists beyond September.