If you are not self-employed and your income will exceed the $200,000 threshold, your employer is required to withhold the additional tax amount over that threshold. Couples who are filing jointly and likely to reach the $250,000 threshold together should adjust their individual income tax withholding to cover the additional tax amounts. Please note that while you can adjust your income tax withholding amounts, you cannot designate additional withholding expressly for the additional Medicare tax. It's important to speak to a professional tax advisor on this and all tax issues.