The additional 0.9% Medicare tax for high earners is based on which income figure?

whole total pay? Gross income adjusted for inflation? or income subject to taxation (after the standard deduction)?

If one is right at the $200k mark, an additional $1800+ for crossing it is a bit of a jump.

If you’re right at the $200k income mark, the additional $1800+ you’re seeing might be due to how income is taxed beyond certain thresholds. Gross income is your total earnings before any adjustments or taxes, while income subject to taxation considers deductions and adjustments. In your case, crossing the $200k threshold could push more of your income into a higher tax bracket, leading to a noticeable increase in your tax liability. It’s essential to consider both the gross income and the income subject to taxation, including how adjustments for inflation or standard deductions impact your taxable income.

Employers do not have to pay the Additional Medicare Tax themselves. However, they are required to withhold an extra 0.9% in taxes from employees who earn more than $200,000 in a year.