Business & farm

According to IRS Pub. 560 - Retirement Plans for Small Business:

Sole proprietors deduct contributions for themselves on Schedule 1, line 15 of Form 1040.  

To do this in TurboTax Home & Business, please follow these steps:

1. On the Business Income & Expenses screen, scroll down to the Less Common Business Situations section and click on the Start/Update box next to Self-Employed Retirement Plans. 
2. On the Self-Employed Retirement screen, click Yes.
3. Click Yes on the next screen, also titled Self-Employed Retirement Plans.
4. Enter the contribution on the screen, Individual and Roth 401(k) Plans, in the elective deferrals box. 

In TurboTax Self-Employed (online)

1. Click on Wages & Income and scroll down to Other Business Situations.
2. Click the Start/Revisit box next to Self-Employed Retirement Plans.
3. On the screen, Self-Employed Retirement Plans click the Yes box.
4. Enter your contribution on the next screen.

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Contributions you make for your employees are deducted on Schedule C. 

You can enter them as employee pension plan expenses in TurboTax using these steps:

1. Go into your business return.
2. On the Here's your [XX] info screen, click the Add expenses box.
3. On the Tell us about any expenses screen, under Less Common Expenses, click the radio button next to Employee pension plan, then click Continue at the bottom of the screen.
4. Enter your contributions to your employees' retirement account on the next screen,  Let's enter the employee pension plan expenses for your [XX] work.