There is not a separate tax rate for Social Security. The taxable amount just adds to your total income and taxed at your regular rate. If your total income increased it can push you into a higher tax bracket. And if you other income increased it will make more of your SS taxable.
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 CD/Download Software you can switch to Forms Mode (click Forms in the upper right) and click on SS in the list on the left side.
