Roth Conversion Toolkit

Roth Conversion Toolkit is an MIT licensed TypeScript library and embeddable widget that prices a Roth IRA conversion the way the tax code actually works, not the way flat bracket calculators pretend it does. A converted dollar is taxed at its bracket rate, and then three more meters run. It can drag another 85 cents of Social Security benefits into taxable income, it can claw back 6 cents of the temporary senior deduction that exists only through 2028, and it can push income over a Medicare IRMAA cliff, where one dollar too many raises premiums for a full year, for each spouse, two years later. The library computes the whole stack at once and reports bracket headroom, effective and marginal rates, cliff distances, and the years left before required minimum distributions close the cheap window. Every figure is read from the primary document, dated in the output, and covered by a test suite of hand computed cases. Zero dependencies, no network calls, nothing leaves the browser.