Category Breakdown

Recalled spending and recorded spending tend to diverge, and they diverge in a predictable direction. Categories with many small transactions get underestimated, because the estimate is built from memory of individual purchases rather than from a total.

Transactions arrive with a merchant-derived category attached, and any of them can be reclassified. That matters for retailers that sell across categories, where a single store visit could reasonably be groceries or household goods depending on the basket.

Concentration is the useful property here. The top two or three categories generally account for around half of all spending, so the totals worth checking carefully are few and the long tail rarely changes the picture.