is my 403-b retirement considered provisional income when it comes to social security for income tax?

Answer 1

Your 403b distributions can cause your SS benefits to be taxed. The number to figure is

Income + 1/2 (SS benefits)

Where income means your 403b plus other income subject to tax other than SS. If this number is over $25K if your are single or $32K if your are married, some of your SS benefits is taxed.

Answer 2

There's no such thing as "provisional income" when it comes to US taxes. Depending upon your other income, up to 85% of your SS income may be taxable. Distributions from your retirement fund count as other income for this purpose.