Per IRS Publication 946 How to Depreciate Property, page 22:

When Must You Recapture the Deduction?

You may have to recapture the section 179 deduction if, in any year during the property's recovery period, the percentage of business use drops to 50% or less. In the year the business use drops to 50% or less, you include the recapture amount as ordinary income in Part IV of Form 4797. You also increase the basis of the property by the recapture amount. Recovery periods for property are discussed under Which Recovery Period Applies? in chapter 4.

CAUTION!  If you sell, exchange, or otherwise dispose of the property, do not figure the recapture amount under the rules explained in this discussion. Instead, use the rules for recapturing depreciation explained in chapter 3 of Pub. 544 under Section 1245 Property. For qualified real property, see Notice 2013-59 for determining the portion of the gain that is attributable to section 1245 property upon the sale or other disposition of qualified real property. You can find Notice 2013-59 at IRS.gov/irb/2013-40_IRB/ar14.html.

CAUTION!  If the property is listed property (described in chapter 5), do not figure the recapture amount under the rules explained in this discussion when the percentage of business use drops to 50% or less. Instead, use the rules for recapturing excess depreciation in chapter 5 under What Is the Business-Use Requirement.

To enter recapture amounts in the TaxAct program:

1. From within your TaxAct return (Online or Desktop), click Federal, then click Income (on smaller devices, click in the top left corner of your screen, then click Federal).
2. Scroll down, and click Review next to Other gains or losses, then click + Add Form 4797 to create a new copy of the form or click Edit to edit a form already created (desktop program: click Review instead of Edit).
3. On the screen titled Asset Sale - Assets Sold, click No. On the screen titled Form 4797 - Other Topics, click Yes
4. On the next screen titled Form 4797 - Other Topics, click the checkbox next to Check here to enter recapture amounts under sections 179 and 280F(b)(2) when business use drops to 50% or less.
5. Continue with the interview process to enter your information.