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Most useful things to send

A rate, bracket, deduction, or cap that disagrees with an official publication. Include the state and a link to the document if you have it; we check against primary sources and correct the data.
A local tax the calculator should offer for your state.
A paycheck that does not reconcile. Send the inputs (not personal details) and what your stub shows; the "How we calculate this" section on each state page explains the formula we applied.

We read everything. Replies to corrections are usually quick; feature ideas go on the list.