You are holding two pieces of paper about the same care and they do not look like each other. The hospital's itemised bill lists services with codes, units and prices. Your insurer's Explanation of Benefits lists the same care with different words, in a different order, under columns called billed, allowed, plan paid and your share. Nobody sits down and reconciles those two documents line by line, because it is slow, fiddly arithmetic on a day when you are already worn out — and that is exactly why the difference between them goes unexamined.

This file does that reconciliation. You put in the lines from both papers — paste the tables rather than typing them — and it matches them up by date and code, checks the arithmetic inside each document, and prints every place they differ. The headline is the comparison most people came for: what the bill is asking you to pay, against the "your share" column of the EOB added up, and the difference between the two. Medicare's own guidance states the principle plainly — your bill should not be higher than the patient balance on the EOB, and the "your share" amount should be the same on both papers.

Everything else on the findings screen is arithmetic, written out so you can check it: a bill line with no matching line on the EOB, so on these two papers it has no counterpart; the same line billed twice on one date; units times unit price that does not give the line total; lines that do not add up to the printed total; an EOB line where plan paid plus your share does not come to the allowed amount; deductible, coinsurance and copay that do not add up to your share; the same service showing different units on the two papers.

What this file will not do is tell you what any of that means for your case. It does not say a bill is wrong, unlawful or dishonest — it shows two figures that differ and the arithmetic between them, and a difference can have an ordinary explanation: a second EOB not issued yet, a line still in processing, a payment already made. It gives no medical, legal or financial advice, promises no money back, and contacts nobody on your behalf. It hands you the figures and the question to ask; the billing office and your insurer are who can answer it.

It runs entirely on your own device. There is no account, no subscription and no upload: the file contains no network code at all, which you can verify yourself by opening it in a text editor and searching for the four letters that start every web address. For medical figures that is not a convenience, it is the point — the services that do this work for you take a share of whatever comes of it and need your records to begin.

The arithmetic exists in two independent versions — the code inside the file, and a separate program written from the written rules rather than from that code, and built the opposite way round. Before packaging, both are run over hundreds of cases, including the awkward ones: brackets used as a minus, a duplicate that differs by a single cent, a percentage typed where an amount belongs, a bill asking for less than the EOB says you owe. Every figure of every answer has to match, or the file is not produced. The count from the run that made your copy is printed in the second PDF.