The taxable amount is shown on line 5b of form 1040. The total amount of social security (from form SSA-1099 is shown on line 5a. If lines 5a & 5b are blank, none of your SS was taxable. (assuming you entered the SSA-1099 correctly).
When TurboTax (TT) prints out your return, it will provide you with the IRS social security worksheet (abbreviated social sec on the forms list) showing you how the taxable amount was calculated. Here’s a blank showing you how the calculation is done: https://www.irs.gov/pub/irs-prior/i1040gi--2018.pdf#page=33 (2018)
Social security only becomes taxable
when added to sufficient other income. If you are otherwise required to file a tax
return, you do need to enter it in Turbotax (TT). TT will determine the taxable
portion.
For the first $9,000 (12,000 MFJ), only 50% of your SS is taxed. After that 85% is taxed. And gradually the 50% taxed is replaced with the 85%. It's the government; they make it complicated. See IRS Publication 915.
Social security (including SSDI) becomes taxable when your income,
including 1/2 your social security, reaches:
Married Filing Jointly(MFJ): $32,000
Single or head of household: $25,000
Married Filing Separately and lived with your spouse at any
time during the tax year: $0
How
much is "sufficient other income"?
The simple answer is $12,000 (a single person's filing requirement). But the answer
varies dependent on marital status, filing status, age, the amount of your Social
security, and whether you are claimed as a dependent by someone else.
