If you earned interest from a bank or brokerage account in 2017, then you should already have received your annual 1099-INT form. Most financial institutions are fairly quick about getting this information to you by the Jan. 31 deadline, although some brokers try to wait until they have all of the data they have to report to the IRS ready at the same time.

For most taxpayers, Form 1099-INT is easy to understand, but there's a lot of detail that can complicate things in some cases. Here, you'll find a box-by-box guide to the 1099-INT form.

Image source: IRS.

Left-side boxes: Personal information

Information about the paying entity as well as your personal information gets put on the left side of Form 1099-INT. Your account number is also included, along with check-boxes to indicate if your financial institution thinks that your account falls under the Foreign Account Tax Compliance Act requirements or if you might have provided an erroneous tax identification number in the past.

Box 1: Interest income

Box 1 indicates any taxable interest income you've received from this payer that doesn't qualify for inclusion under Box 3. That typically includes interest on bank savings accounts and CDs as well as corporate bond interest.

Box 2: Early withdrawal penalty

If you took a withdrawal from a bank CD before it matured, you typically have to pay a penalty, and any amount you paid will show up here. You're allowed to deduct early withdrawal penalties against your gross income on your tax return to reflect the fact that your financial institution kept part of the interest you had earned.

Box 3: Interest on U.S. Savings Bonds and Treasury obligations

Box 3 includes all interest from obligations of the U.S. government, including Treasuries and savings bonds. This interest is generally taxable at the federal level but qualifies for favorable tax-free treatment on state returns, so it's helpful to know how much income comes from those sources.

Box 4: Federal income tax withheld

Any federal income tax that your bank or broker withheld on your behalf will show up in Box 4. Be sure to count this amount under the payment section of your tax return to calculate your refund or amount owed correctly.

Box 5: Investment expenses

If there are deductible investment expenses that the financial institution incurred on your behalf, then they'll be listed here. Keep in mind that some expenses get directly deducted from income and therefore don't show up here. This box typically applies only for a special class of investments known as real estate mortgage investment conduits.