You don’t calculate that yourself. Turbo Tax automatically calculates the taxable amount. Did you enter the full amount of SS? Social Security is on 1040 line 6a and any taxable amount on 6b. Seems odd the IRS gave you a refund. Usually they say you didn’t report the right taxable amount and owe more tax.
If you calculated it yourself where or how did you enter it?
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.
Or use the IRS worksheet in the 1040 instructions page 32
https://www.irs.gov/pub/irs-prior/i1040gi--2024.pdf
