An individual can claim their spouse's exemption if using the filing status Head of Household or Married Filing Separately, and only when specific conditions are met. In the TaxAct® program, this entry is made on the screen titled Spouse Exemption in the Basic Info section.
Per IRS Instructions for Form 1040, page 15:
Check the box on line 6b if either of the following applies.
If your filing status is head of household and you check the box on Line 6b, enter the name of your spouse on the dotted line next to Line 6b. Also, enter your spouse's social security number in the space provided at the top of your return. If you became divorced or legally separated during 2017, you can't take an exemption for your former spouse.
If you are filing as head of household and are qualified to claim the spouse exemption:
The spouse's social security number must be entered in order to see the Head of Household Information option. If you are not prompted to enter the spouse information, it can be entered in the Name and Address section of Basic Information.
If you are filing as married filing separately and are qualified to claim the spouse exemption:
For more information about selecting a filing status, click IRS Form Instructions on the right side of the screen.