Retirement tax questions

I have read that depending on your income and a number of factors, you could have 50% of your total Social Security Income taxed, or it could be as high as 85% taxed.  Is it a sliding scale such that it could be a percentage between 50% and 85%?     If I look at my 1040-SR that TurboTax created for me and divide box 6b by box 6a, I come out to a little over 55%.   Can that be correct?