You probably already have the standard deduction for your filing status for tax year 2018.  Look at your tax return.  Click on Forms in the upper right of the desktop program screen.  Click on Form 1040 on the left side of the screen.  On Line 8 is either your standard deduction or your itemized deduction.

Standard deductions for 2018

• Single - $12,000 add $1,600 if age 65 or older
• Married Filing Separately - $12,000 add $1,300 if age 65 or older
• Married Filing Jointly - $24,000 add $1,300 for each spouse age 65 or older
• Head of Household - $18,000 add $1,600 if age 65 or older

If you are Married Filing Separately, you must also tell TurboTax that neither you nor your spouse is itemizing deductions.  When Married Filing Separately, if one spouse itemizes the other spouse must itemize.  Revisit the Spouse information under You & Your Family in the Personal Info section.