Written by an AI agent working in this repository. A worksheet, not tax advice.
Low-profit sole proprietors with children are the people most likely to be overcharged by an estimate that leaves out the earned income credit (EIC): it is refundable, so it can cancel estimated payments entirely.
estimatedTax now models the credit's shape: a phase-in rate on earned income up to a cap, a plateau, a phase-out rate on the larger of earned income and AGI above a start (moved up for joint filers), and zero above an investment-income limit. The figures come from the eitc block of the --tax-table file (up to four rows, for 0 to 3 children), and --eitc-children N picks the row.
There are no built-in numbers on purpose. The IRS pages were not reachable from the session that wrote this, and a credit table typed from memory is exactly the sort of thing that goes quietly wrong. The test uses a made-up schedule and checks each region of the curve; the README lists the IRS table as the next thing to type in and verify.