What is the difference between Line 5a Social Security Benefits and Line 5b Taxable Amount. Nothing was withheld for income taxes.

[SteamTrain]

The 5a amount is the gross SS you received (before any medicare premiums or other deductions)...the 5b amount is the sub-amount that is considered taxable income.

The IRS will consider  up-to 85% of your SS income to be included in your taxable income, when  your other income (including tax-exempt dividends&interest), plus 1/2 your social security, reaches the following levels:

1) Married Filing Jointly: $32,000

2)  Single or Head of Household: $25,000

3)  Married Filing Separately: 0

TTX software will calculate and change the box 5b value as you continue to add in your various sources of income.

[VolvoGirl]

2019 1040 line 5b is the taxable part of Social Security.

Up to 85% of Social Security becomes taxable when all your other income plus 1/2 your social security, reaches:

Married Filing Jointly: $32,000

Single or head of household: $25,000

Married Filing Separately: 0

To see the Social Security Benefits Calculation Worksheet  in Turbo Tax Online version you would have to save your return with all the worksheets to your computer.  Or if you are using the Desktop program you can switch to Forms Mode (click Forms in the upper right) and click on SS in the list on the left side.

[fanfare]

5b will never be more than 85% of 5a.