Why do I get a credit for "Excess social security and tier 1 RRTA withheld" while not working for railroad company?

It depends. If you worked for the railroad and worked at another job where social security was being withheld, then you may have overpaid the maximum amount required in 2024. TurboTax would automatically calculate this for you based on your W-2 entry. It only occurs on your tax return when more than one employer is involved. 

• IRS Topic 608 - Excess Withholding
• See Schedule 3, Part II, Line 11: Excess social security and tier 1 RRTA tax withheld
• See Form 1040, Line 31: This is added like a payment on your tax return

With only one employer an employee must go back to the employer for the refund because it would never be paid to the IRS based on the employer tax forms.

• Maximum wages subject to social security tax in 2024 = $168,600 ($176,100 for 2025).