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.
Social security (including SSDI) becomes taxable when your income, including 1/2 your social security, reaches $32,000 (Married Filing Jointly(MFJ)).
For the first $12,000, after that, 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. When TT prints out your return, it will provide you with the IRS social security worksheet showing you how the taxable amount was calculated. Here’s a blank copy showing you how the calculation is done:
https://tax.thomsonreuters.com/content/dam/ewp-m/documents/tax/en/pdf/other/quickfinder-updates/qpep...
After TurboTax (TT) calculates the taxable portion of SS, it puts the total amount of SS on line 5a of form 1040 and the taxable amount on line 5b
