Lots of wage earners only file tax returns once a year. But small business owners, including the self-employed, have additional taxes to worry about–and possibly year round.

While many wage earners only concern themselves with taxes on one day of the year, small business owners often have filing requirements all year round. In addition to income tax returns, you may be required to file and pay payroll taxes, sales and use taxes, excise taxes, and more—on the federal, state, and local levels. It’s a lot to juggle. And while I’m a big proponent of having a team to help with tax matters, you should still be aware of what—and when—to file. Here's a quick summary of what you need to know.

Most businesses will need an Employer Identification Number (EIN) — think of it as your business's Social Security Number. This number is what you'll use to open your bank account and file your tax returns.

You typically need a new EIN when starting a business or if you change the structure of your business, such as converting from a partnership to a corporation. You don’t typically need a new EIN if you merely change your business name or address. Additionally, sole proprietors or single-member limited liability companies that file taxes using Schedule C (on a 1040) and don’t have employees or owe excise tax do not need an EIN.

It’s easy to apply for an EIN, and it’s free. Some companies or professionals may charge a fee for obtaining an EIN for you, but this should reflect the time or service provided. The Internal Revenue Service does not charge a fee for an EIN.

The fastest way to get your EIN is online directly through the IRS website.

To apply online, your principal place of business must be located in the U.S. or its territories, and you must be the responsible party with a valid Social Security number (SSN) or Individual Taxpayer Identification Number (ITIN). If you’re a third-party designee, you must have a signed authorization (like Form 2848) to apply.

You can also fax Form SS-4, Application for Employer Identification Number, to 855.641.6935 (for U.S. businesses). If you apply by fax and provide a fax number, the IRS will fax a cover sheet with the EIN back to you in........

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