I am filing my taxes and it says my employer withheld too much social security, that I need to contact my employer to get a corrected W-2. How can I prove to my employer?

How much is in box 4 on your W2?   First of all try leaving the cents off box 4.  Check boxes 3 & 4 on your W2. Box 4 should be 6.2% of box 3 up to a max of $9,932.40. So take the amount in box 3 and multiply it by .062. If box 4 is more than that you need to get a corrected W2 from your employer. But also go back and double check your W2 entries, you may have entered box 3 & 4 wrong. A lot of people who have asked this found they did enter an amount wrong.

Or check W2 box 12. You may have entered Code A by mistake.

A sure way to fix this is to delete the W2 and re-enter it. That may clear something out.

If your W-2 has an amount in box 7, then box 4 should be 6.2% of the total of box 3 and box 7, but not more than $9,932.40.

Do you have only one W-2 in your tax return?