Does Turbo Tax have a calculator for figuring out max SE 401K deduction? (maximum standard deferral ($18500 for 2018) + .25% of earned income)

Yes, there is a tool within TurboTax to help you determine how much you can contribute.

Use the steps below to go to the self-employed retirement section of your return.  Go through the screens until you get to the question regarding making a contribution to an individual 401k where you will indicate that you have (or are) contributed.  Then, there will be a check-box near the entry for the amount you contributed or plan to contribute.  The box is labeled Maximize.  Checking the box will allow TurboTax to calculate the maximum that you can contribute based on your business income.

• On the top row of the TurboTax online screen, click on Search (or for CD/downloaded TurboTax locate the search box in the upper right corner)

• This opens a box where you can type in “self-employed retirement” (be sure to enter exactly as shown here) and click the magnifying glass (or for CD/downloaded TurboTax, click Find)

• The search results will give you an option to “Jump to self-employed retirement”

• Click on the blue “Jump to self-employed retirement” link

Also, the maximum permissible employer contribution is not 25% of earned income.  The maximum permissible employer contribution for the self-employed individual is 20% of the result of subtracting the deductible portion of self-employment taxes from net profit.  Depending on the amount of profit and self-employment tax, you might also be limited to less than that.