If is taxed if your "non benefit" income is more than $25,000 on a single return or $32,000 on a joint return.
If that income is between $25,000 and $34,000 on a single return or between $32,000 and $44,000 on a joint return, up to 50% of your benefits can be taxed. The rest is tax-free.
Now, if your "non benefit" income is more than $34,000 on a single return or $44,000 on a joint return 85% of your benefits will be taxed.
If you just retired then it probably won't be that much considering your payroll withholding before you retired assumes you worked the full year, and it will just slightly reduce any tax refund you might be getting, but you can get the 2016 tax software and enter your best income estimate and see how much it could be. I certainly wouldn't bother going through the trouble of getting an estimate assuming you just retired this December.
The government does not give anyone on social security a free pass. If it's considered an income, it's going to be taxed. Doesn't make much sense, but it is.
If you just retired so you worked most of the year, 85% is probably taxable, at whatever your marginal rate is.
If you give your filing status, amount of SS, and amount of other income, anyone answering questions here could give you the exact amount of your taxable SS. They could give you the amount of tax on it if there are no extenuating circumstances.
You can estimate it now if you want.