Every Monday morning, one economics student records what the same fixed basket costs at three Folsom grocery stores — Walmart, Target, and Safeway — item by item, straight from each retailer's own published store prices. National CPI tells you what food costs on average, months later. This tells you what it costs here, this week — measured, not estimated.
data/prices.csv with your first real collection to go live.
FOLSOM, CA — HYPERLOCAL CPI
WEEK OF —
*** THANK YOU FOR READING ***
01 — The number
The index is a weighted average of price changes across five food categories, benchmarked to the first week of the official series (= 100). Weights are fixed, BLS-style food-at-home category weights, published in the page source, so a move in this line means the same thing a CPI move does — just for Folsom, and weekly instead of monthly.
The official series begins Aug 24, 2026 (= 100). The seven weeks of Jul 6 – Aug 17 were a pilot used to finalize the collection protocol; pilot observations are published in the raw CSV, flagged pilot, and excluded from the index — details in the revision log.
02 — The spread
The exact same basket, rung up at each store this week. The gap between the cheapest and priciest cart is real money a family keeps by driving five extra minutes.
Based on this week's percentage gap between the priciest and cheapest cart, applied to your own grocery budget.
03 — The shelf
Average shelf price across all tracked stores for each basket item, with the week-over-week move. These are the tags shoppers actually see.
04 — The method
The same named items, in the same package sizes, at the same stores — every single week. No substitutions; if an item is out of stock, it's flagged and its prior-week price is carried forward (standard index imputation), never substituted. The two meat items are specified exactly: store-brand conventional 80/20 ground beef and boneless-skinless chicken breast, priced per pound from the standard tray closest to one pound — never value packs, chubs, or premium lines.
Prices recorded every Monday morning from each retailer's own website or app, with the exact Folsom store location selected. Prices are recorded as displayed for that store, including free loyalty-program pricing where the retailer shows it (Safeway for U); clip-to-activate coupons and paid-membership prices are never used.
Category price relatives are combined with BLS-style food-at-home weights (a Laspeyres index), so the composite behaves like a true price index, not a raw price average.
Every observation lives in a public CSV on GitHub. Anyone can audit the math, rebuild the index, or extend it to their own city.
pilot, and are excluded from the index.archive/belair.csv.per banana).This is an independent student research project. It is not affiliated with, endorsed by, or informed by any retailer's internal data — every price is the retailer's own publicly listed price for its named Folsom store. Store names can be anonymized on request.