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Written from the bugs, not from a textbook
Guides to reading a filing without getting a wrong number
Every one of these started as something that broke in our own code, got traced back to a filing, and turned out to be a trap anyone building a valuation from SEC data walks into. The figures in them are read live from EDGAR and the scripts that produced them are published alongside, so nothing here has to be taken on trust.
Which XBRL tag is free cash flow, and why the obvious one is wrong
Free cash flow is two tags subtracted, and both have aliases that large companies quietly abandoned years ago. The abandoned tag keeps answering. Amazon's returns $6,737m from 2016 next to the real $131,819m from 2025, and AT&T's stale figure is within one percent of the right one, which is far more dangerous. A survey of twenty large filers, with the rule that fixes it.
14 October 2026 · 20 companies · evidence
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One guide a week. Coming up: which share count belongs in a DCF, the cover-page count or the diluted weighted average, and why picking the wrong one valued a real company at five dollars instead of ninety-five. After that: what to do when terminal growth is above your discount rate.
Rather use the arithmetic than read about it? The calculator applies these rules to any SEC filer and names the tag behind every figure it fills in.
Open the calculator