You will need to switch to Forms Mode to use this worksheet. In the top left corner of your MAC program, you should see an icon that says Forms - click this icon. Then, click the option to Open Form and search for "what-if worksheet" under the Form 1040 option. See attached screenshots for a visual. This section is commonly used to compare MFS vs MFJ.
Note: You may also be referring to the Estimated Taxes section where you can add or subtract income and see if you should make estimated tax payments. If this is what you are really looking for, then you can review that section by following the steps below (or use the search feature and search for "W4")
- Click Federal Taxes
- Click Other Tax Situations
- Scroll down to Other Tax Forms
- Select Form W4 and Estimated Taxes
