Connecticut Bonus Tax Calculator 2026

Connecticut only allows the aggregate method

Informational Publication 2026(1), the Connecticut Employer's Tax Guide known as Circular CT, gives a single rule for a bonus paid on its own: if tax was withheld from regular wages, "the employer must compute the tax on the combined regular and supplemental wages. The computed tax minus the tax withheld from regular wages is the tax to be withheld from supplemental wages." The calculation rules state plainly that "there is no percentage method available." The guide's own example adds the bonus to the last regular pay period.

Five tables and a CT-W4 code

Connecticut's 2026 withholding calculation rules (TPG-211, unchanged from 2025) run annualized wages through Table A (personal exemption, which phases out), Table B (initial tax from 2% to 6.99%), Table C (the 2% rate phase-out add-back), Table D (tax recapture) and Table E (personal tax credit). Which column applies depends on the withholding code on your CT-W4: F for single filers above $15,000, B for heads of household, A or C for married couples depending on whether the spouse works, and D for the highest withholding. For the standard example, code F, the bonus carries $318.65; a married employee on code A sees $313.85.

Because exemptions and credits shrink as annualized pay rises, the extra tax on a bonus can exceed 6.99% of it for people inside those phase-out ranges. A $30,000 bonus on top of a $9,000 biweekly paycheck is withheld $2,182.25.

No CT-W4 on file

An employee who never completed a CT-W4 is withheld "at a flat rate of 6.99%, without allowance for exemption" — $349.50 on the standard bonus. Filing the form is the simplest way to bring bonus withholding back in line with your actual Connecticut bracket.