Updated October 24, 2026. Quick answer: Tax Topic 608 is the IRS page on excess Social Security and railroad retirement (RRTA) tax withheld. It separates two cases. If one employer withheld too much, the employer should adjust it. If you had more than one employer, the topic says you may be able to claim the excess as a credit on your income tax return.
Quick reference
| Item | What the IRS topic says |
|---|---|
| Who withholds | “Most employers must withhold Social Security tax from your wages.” |
| One employer withheld too much | “Your employer should adjust the excess for you.” |
| Employer does not adjust | “you can use Form 843, Claim for Refund and Request for Abatement to claim a refund” |
| Two or more employers | “you may be able to claim the excess as a credit against your income tax on your income tax return.” |
| Tier 2 RRTA | “you may request a refund of the excess tier 2 RRTA tax using Form 843” |
| Joint returns | “you and your spouse must figure any excess Social Security tax or tier 1 RRTA tax separately.” |
Who withholds Social Security and RRTA tax
The topic starts with the basic rule. The IRS topic says “Most employers must withhold Social Security tax from your wages.” It also says “Certain government employers (some federal, state and local governments) don’t have to withhold Social Security tax.”
For railroad workers, it says “If you work for a railroad employer, your employer must withhold tier 1 railroad retirement tax act (RRTA) tax and tier 2 RRTA tax.” It explains the tiers: “Tier 1 RRTA provides Social Security and Medicare equivalent benefits, and tier 2 RRTA provides a private pension benefit.”
When one employer withheld too much
The topic calls this an employer’s error. It says “If any one employer withheld too much Social Security, tier 1 RRTA tax, or tier 2 RRTA tax, you generally can’t claim the excess as a credit against your income tax.” The fix it names is “Your employer should adjust the excess for you.”
If that does not happen, the topic says “you can use Form 843, Claim for Refund and Request for Abatement to claim a refund”. It also says “Attach copies of your Forms W-2, Wage and Tax Statement for the year to Form 843.” Box 4 of the W-2 is explained on our W-2 box 4 page.
When you had more than one employer
The topic describes how excess can arise: “If you had more than one employer during the taxable year and your total wages and compensation were over the wage base limit for the year, the total Social Security tax or Social Security equivalent tier 1 RRTA tax withheld may have exceeded the maximum amount due for the tax year.”
For the credit route, the topic says “If you had more than one employer and too much Social Security tax or tier 1 RRTA tax withheld, you may be able to claim the excess as a credit against your income tax on your income tax return.” For tier 2 it says “If you had more than one employer and too much tier 2 RRTA tax withheld, you may request a refund of the excess tier 2 RRTA tax using Form 843”.
The credit is entered on Schedule 3 line 11. On the wage base, see our Social Security wage base page. For married filers, the topic says “If you’re filing a joint return, you and your spouse must figure any excess Social Security tax or tier 1 RRTA tax separately.”
Where this comes from
This page describes the IRS page titled Topic no. 608, Excess Social Security and RRTA tax withheld, as served on irs.gov on October 24, 2026. The IRS page shows that it was last reviewed or updated on 16 Oct 2026. The IRS can change a topic after we read it, and the IRS page controls. General information, not tax or legal advice.
Common mistakes
- Claiming a credit for a single employer’s mistake. The topic says “you generally can’t claim the excess as a credit against your income tax”
- Treating all excess the same way. For tier 2, the topic says you “may request a refund of the excess tier 2 RRTA tax using Form 843”
- Combining spouses’ wages. The topic says “you and your spouse must figure any excess Social Security tax or tier 1 RRTA tax separately”
- Assuming every employer withholds. The topic says “Certain government employers (some federal, state and local governments) don’t have to withhold Social Security tax.”
Related: IRS tax topics by number, Schedule 3 line 11: excess Social Security tax withheld, W-2 box 4: Social Security tax withheld, W-2 box 3: Social Security wages, and Social Security wage base for 2027.
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Answer againSources
- IRS, Topic no. 608, Excess Social Security and RRTA tax withheld (irs.gov): https://www.irs.gov/taxtopics/tc608
- IRS, Tax topics index (irs.gov): https://www.irs.gov/taxtopics
Read from the IRS pages linked above on October 24, 2026. General information, not tax or legal advice. The IRS topic page and the instructions for your own form control, and your own facts decide the outcome.