• your net earnings are $400 or more, or
• you performed services for a church as an employee and received at least $108.28.

Paying income taxes as you go
The federal income tax is a pay-as-you-go tax. You must pay the tax as you earn or receive income during the year. If you do not pay your tax through withholding (e.g., an employee has income tax withheld from his or her pay), you might have to pay estimated tax. Sole proprietors, partners and S corporation shareholders have to make estimated tax payments if they expect to owe tax of $1,000 or more. Corporations have to make estimated tax payments if they are expected to owe $500 or more.

Tax year
You must figure taxable income on the basis of a tax year. You can use a calendar year or a fiscal year as your tax year. Your tax year also determines when your taxes are due. The due date for sole proprietors, partners and S corporation shareholders is the 15th day of the fourth month after the end of the tax year. The due date for filing returns for corporations and S corporations is the 15th day of the third month after the end of the tax year.

Income taxes on a sole proprietorship
If you are a sole proprietor, after subtracting business expenses from business revenue you'll figure the personal tax you owe on Schedule C, which you'll include with Form 1040 and file once a year.

Income taxes on a partnership
A partnership files a report of annual revenue and expenses with Form 1065, U.S. Partnership Return of Income, but no tax is due with this form. Instead, each partner divides the profits or losses as specified in the Partnership Agreement and adds this information to the Schedule E, Supplemental Income and Loss, which he or she then files with his or her individual 1040 form.

Income taxes on a corporation
Both kinds of corporations file tax forms once a year, and most forms must be received by the Internal Revenue Service by March 15. There are exceptions, but for most American corporations, this is the rule. The similarity ends there, however. A regular C corporation reports revenue and expenses on Form 1120, or the short Form 1120A. A subchapter S corporation files Form 1120S, but is not responsible for taxes on profits and doesn't receive a credit in the case of a loss. Instead, an S corporation splits the profits among each of its shareholders, who then receive a Schedule K-1 that lists their share of the income. The shareholders then include this information on their individual 1040 Forms along with Schedule E.

Income taxes on a limited liability company
An LLC with two or more members is automatically taxed as a partnership; however, it can elect to be taxed as a corporation. A single-member LLC is taxed as a sole proprietorship unless it elects to be taxed as a corporation. The election is made on Form 8832, Entity Classification Election. If the LLC is being taxed as a partnership, it files Form 1065.

Lowering your taxes
The good news is that nearly every single penny you spend in the course of doing business can be deducted from your overall business revenue, which in turn will reduce the amount of tax you'll have to pay the federal government. A warning here: In most cases, equipment, capital improvements and business vehicles are not totally deductible all at once, but either partially or in stages. So before you head out to purchase a brand new copier or computer for your business, check with your accountant to see when you'll be able to deduct it and in what amount.

Facing a tax audit
Tax audits are not fun. No one wants to be faced with a tax audit, but it is a possibility for all businesses. While there is no way to be sure your business will escape an audit, there are things you can do to reduce your odds of getting audited and to survive an audit if your business is chosen.