Flat 5% - until the millionaire line
Massachusetts runs a flat 5.00% income tax with one famous exception: income above $1,107,750 (the 2026 threshold, inflation-adjusted yearly) pays an extra 4% surtax - the "millionaires tax" voters added to the constitution. For most paychecks the math is simply 5% of taxable income; for very high earners the calculator above applies the 9% combined rate on the excess automatically.
The line most workers actually notice is smaller: Paid Family and Medical Leave. The employee share runs 0.46% of wages up to the Social Security cap ($184,500) - a deduction several national calculators still omit, which is why our Massachusetts number can differ from theirs by exactly that premium. Ours matches the stub; the receipts are on the methodology page. Employers are allowed to pay part or all of the employee share, so your own stub may show less than the calculator assumes.