There is no need for you to calculate the taxable amount of your SS benefits. When you enter box 5 from the SSA-1099 and you also have other taxable income reported, the TurboTax program does the calculation and enters the taxable amount, if any, on your Form 1040 Line 6b.
TurboTax uses the same worksheet to calculate the taxable portion that is in IRS Publication 915 Social
Security and Equivalent Railroad Retirement Benefits - https://www.irs.gov/pub/irs-pdf/p915.pdf#page=16
