Code A: If your employer could not collect all the social security taxes you owe on tips you reported for the year - for example if your regular pay was not sufficient to cover the taxes you owe - the amount of uncollected social security tax on tips will be reported here. You will need to include these taxes in the Total Tax line on Form 1040, and write "UT" and the amount of the uncollected social security taxes on the dotted line next to the Total Tax line. In this case, you will need to file a return (1040, not 1040A or 1040EZ) and pay these taxes even if you otherwise would not have to file a return.
Code B: Uncollected Medicare tax on tips. This item is the same as code A but for Medicare instead of social security, and should be handled the same way.
Code C: If your employer provides you with group-term life insurance, the cost of the coverage in excess of $50,000 is taxable. This taxable amount is included in box 1 and is reported here for informational purposes. The cost of coverage up to $50,000 is not taxable.
Code D represents the amount of your salary you choose to have your employer contribute to a qualified retirement fund rather than pay to you. Code D is for elective deferrals to a section 401(k) cash or deferred arrangement. It also includes deferrals under a SIMPLE retirement account that is part of a section 401(k) arrangement. This amount is not included in your salaries and wages subject to tax at the time contributed.
Code E is similar to code D but corresponds to elective deferrals under a section 403(b) salary reduction agreement.
Code F: Elective deferrals under a section 408(k)(6) salary reduction SEP (Simplified Employee Pension).
Code G: Elective deferrals and employer contributions (including non-elective deferrals) to a section 457(b) deferred compensation plan.
Code H: The contributions you make as elective deferrals to a section 501(c)(18)(D) tax-exempt organization plan should not have been deducted from your total salaries and wages as reported in box 1. This amount can be taken as a deduction for adjusted gross income. You should enter “501(c)(18)(D)” and the amount on the dotted line right above the line for Adjusted Gross Income” on Form 1040.