What Is a W2 Form and Why Does It Show Up Every January?

Every January, something arrives in your mailbox or email inbox that a lot of people find stressful: a W2 form. It's a small document — usually just one page — but it carries a lot of weight because your entire tax return depends on it. If you've ever looked at a W2 and felt unsure what you were looking at, this guide will walk through every part of it in plain, honest language.

What a W2 actually is

A W2 is a summary your employer sends you at the end of each year. It tells you — and the IRS — exactly how much you earned and how much was withheld in taxes throughout the year. Your employer is required by law to send it to you by January 31st. If you had more than one job during the year, you'll receive a separate W2 from each employer. You need all of them before you file your taxes.

Box 1 — Wages, tips, other compensation

This is your total taxable income for the year from that employer. It sounds like it should match your gross pay from your last pay stub of the year, but it often doesn't — and that's normal. The reason is that certain deductions like 401(k) contributions and health insurance premiums paid through your employer are taken out before this number is calculated. So Box 1 is actually lower than your total gross earnings, which in most cases means you owe less in taxes.

Box 2 — Federal income tax withheld

This is the total amount sent to the federal government on your behalf throughout the year. When you file your tax return, this number gets compared to what you actually owe. If Box 2 is more than what you owe, you get a refund. If it's less, you owe the difference. This is the box that determines the outcome of your tax filing more than almost any other.

Boxes 3 and 4 — Social Security wages and tax withheld

Box 3 shows how much of your income was subject to Social Security tax. Box 4 shows how much was actually withheld — which should be exactly 6.2% of Box 3, up to the annual wage limit. If you earned above the Social Security wage base (which changes slightly each year), Box 3 will be capped even if Box 1 is higher.

Boxes 5 and 6 — Medicare wages and tax withheld

Similar to Social Security, but Medicare has no wage cap. Box 5 is your total wages subject to Medicare tax, and Box 6 is the 1.45% that was withheld. If you earned more than $200,000, you may see an additional 0.9% Medicare surtax — that would also appear here.

Box 12 — The box with letter codes

Box 12 confuses almost everyone because it uses letter codes instead of plain labels. Some common ones: Code D means 401(k) contributions. Code DD means the cost of employer-sponsored health coverage. Code W means contributions to a Health Savings Account. You don't usually need to do anything with these codes when filing — your tax software or preparer handles them — but it's helpful to know they're not errors.

Boxes 15 through 17 — State tax information

These boxes show your state wages and how much state income tax was withheld. If you live in a state with no income tax, these may be blank. If you worked in multiple states during the year, you may see multiple rows.

What to do when your W2 arrives

First, make sure the name, address, and Social Security number on the form are correct. An error there can cause problems with the IRS. Second, compare Box 1 to your final pay stub of the year — if they're significantly different and you don't know why, ask your HR department before filing. Third, keep all your W2s in one place until your taxes are done.

Freelance and other non-wage income usually arrives on a 1099 instead—here is how the common variants work.

If you'd like a plain English walkthrough of your actual W2 — every box, explained specifically for your document — you can upload it at ReadMyPay.com. Nothing is stored on our servers. Your document is read in your browser and never saved anywhere.