About
Mathstub is a free calculator suite for US tech workers with equity compensation. We solve the math for 8 specific situations off-the-shelf tax software gets wrong or skips: RSU withholding shortfall, ESPP qualifying-disposition decisions, ISO/AMT exposure, AMT credit recovery via Form 8801, NSO bargain-element tax, bonus-tax shortfall, IRC §6654 quarterly estimated tax safe-harbor, and state-by-state stock-comp tax lookup. All math runs in your browser. No account required, no signup, no tracking on the calc pages. Every claim cites the IRS publication and code section. 243 unit tests cover edge cases. Built by a tech worker who lost $6k to an April-surprise underwithholding penalty.