I think you need to assume that 85% of your SS benefit will be taxable. If you have too much withheld, you will get a refund when you file your return.
1. If you work after retirement and earn more than the threshold, your SS benefits will be reduced in the following year. For 2023 the threshold is $21,240. There will probably be an inflation adjustment to the threshold for 2024.
2. You will continue to pay social security and medicare tax on any wages earned, no matter what your age is. That's just how it works.
3. If half your SS benefit plus all your other taxable income (includes wages, IRA withdrawals, pension, lottery, etc.) is more than $25,000, up to 85% of your SS benefit will be taxable (the exact amount depends on your other income and a formula).
