Categorise expenses the same way twice

Expense categorisation is not hard, it is just relentless, and the cost of doing it inconsistently only shows up months later when a category is meaningless because three people filled it three ways.

Consistency is the thing worth automating. The judgement calls are not.

Give it your actual chart of accounts

Not a generic set. Yours, with the notes about what belongs where, including the categories that exist for reasons a newcomer would not guess.

The categories nobody can define are the ones that get filled inconsistently, and writing this down surfaces them before you automate anything.

Categorise the clear ones, hold the rest

Every weekday, categorise new expenses against our chart of accounts.

Assign a category only where it is unambiguous from the merchant and the
description.

Leave anything ambiguous uncategorised and list it for me, with what you
would have guessed and why you were unsure.

Never create a new category. Never use "miscellaneous" or "other" as a way
to finish.

For each one you did categorise, note the reason in a sentence.

Forbidding "miscellaneous" is what makes this work. Given a catch-all, anything uncertain goes there, the uncertain pile becomes invisible, and you discover at year end that eleven percent of spend is uncategorised. Refusing the escape hatch forces the ambiguity to surface as a question while it is still cheap to answer.

The unsure pile is the useful output

Every item in it is a gap in your chart of accounts, found by something that had to make a decision and could not.

Most companies find two or three recurring merchants nobody had decided about. Decide once, add it to the document, and the pile shrinks.

Do not let it touch anything already categorised

A human who categorised something did so for a reason that may not be in the document. Recategorising their work silently is how you lose trust in the whole arrangement.

New entries only.

What good looks like

The clear majority of expenses land in the right place without anyone touching them, and what reaches a person is a short list of genuinely ambiguous items with a suggested answer.

The measure is the size of the unsure pile over time. It should fall for a month as you fill gaps in the chart of accounts, then hold steady.