All wages, salaries and tips you received for performing services as an employee of an employer must be included in your gross income. Amounts withheld for taxes, including but not limited to income tax, social security and Medicare taxes, are considered "received" and must be included in gross income in the year they're withheld. Generally, your employer's contribution to a qualified pension plan for you isn't included in gross income at the time it's contributed. Additionally, while amounts withheld under certain salary reduction agreements with your employer are generally excluded from gross income, such amounts may have to be included in wages subject to social security and Medicare taxes in the year they're withheld. See Publication 17 (PDF), Chapter 5, Wages Salaries and Other Earnings, and Chapter 6, Tip Income, for specific information.
Your employer should provide you a Form W-2, Wage and Tax Statement (PDF) showing your total income and withholding. You must include all income and withholding from all Forms W-2 you receive on your tax return, and if filing jointly, you must also include all income and withholding from your spouse's Forms W-2. Attach a copy of each Form W-2 to the front of your tax return as indicated in the instructions. For information on tips, refer to Publication 531, Reporting Tip Income, Publication 1244, Employee's Daily Record of Tips and Report to Employer (PDF), Topic No. 761, Tips - Withholding and Reporting, and Is My Tip Income Taxable? For information on excess social security or railroad tax withholding, refer to Topic No. 608, Excess Social Security and RRTA Tax Withheld. Please note that self-employment income is generally reported on Form 1099-MISC, Miscellaneous Income (PDF). For more information on business income, refer to Topic No. 407, Business Income and Publication 334, Tax Guide for Small Business.
If you receive a Form W-2 after you've filed your return, file an amended tax return, Form 1040X (PDF). For more information on amended returns, refer to Topic No. 308 and Should I File an Amended Return? Your Form W-2 should be made available to you by January 31, 2019. For information about incorrect Forms W-2 or non-receipt, refer to Topic No. 154, Form W-2 and Form 1099-R (What to Do if Incorrect or Not Received).