Your year-end package told you what the practice made. It didn’t tell you which clinician made it.

• A practice can clear a healthy net while one seat runs underwater. The total nets them together, so the loss shows up as a slightly smaller win and never as a problem.
• Two clinicians can bill nearly the same and net nothing like the same — different splits, different hours, a different share of the rent. There is no line on a practice P&L where that difference can appear.
• The year is closed either way. The open question is what to do differently next year, and every version of that answer is about a particular person in a particular seat.

We are not re-adding your numbers, and finding a mistake is not the point. Bookkeeping answers a question about the practice, and answers it well. This asks a different question of the very same file: not what the practice made, but who made it, and what each seat costs to keep.

• Drop in a CSV with a clinician column, a date, and an amount — the year-end package, an income report out of your EHR, whatever you already have on hand. That is the entire input.
• It is read in your browser. Client names, dates of birth, diagnoses and addresses are dropped before a single figure appears; only provider names and monthly revenue survive. Turn off your Wi-Fi and it still works, because there is no server here to send anything to.
• You get each seat’s fully-loaded net: what is left after that clinician’s pay, the employer share of payroll taxes, and their share of overhead. The overhead figure is the one thing we assume — set it to your real number and everything below it moves.

It is an estimate built from one file and a handful of stated assumptions, not a set of books. The point is the shape of the gap between seats, which is usually wider than anyone expects.