21 — Three or More Children Social Security Excess Updated for tax year 2025

What this line means

An alternative method for computing the additional child tax credit available only to filers with three or more qualifying children. You take the total Social Security and Medicare taxes paid (both employee and self-employment portions) and subtract the earned income credit received. If this amount exceeds the line 20 result, you can use it instead to get a larger refundable credit.

Does this apply to you?

• You have three or more qualifying children on line 16
• You want to check whether the Social Security tax method produces a larger refundable credit than the 15% earned income method
• You have low earned income but paid significant FICA taxes

Easy to overlook

This method can help families with very low earned income A family earning $5,000 with three children gets only $375 from the 15% method ($5,000 minus $2,500 times 15%). But if they paid $383 in Social Security and Medicare taxes and claimed no EIC, the Social Security method would yield $383 — slightly more. In practice, most families with three children and $5,000 of income would also claim the EIC, which reduces the Social Security method result. The difference between methods grows with higher FICA taxes and lower EIC claims. ¹ [SOURCE: IRC Section 24(d)(1)(B)(ii) — alternative computation for three or more children]

You subtract the earned income credit from the Social Security taxes The EIC reduces the Social Security tax amount in this calculation. If you claimed a large EIC, the Social Security method may produce a smaller number than the 15% earned income method. You must run both calculations and take the larger one on line 22. ² [SOURCE: IRS Schedule 8812 instructions — Social Security tax excess method]

Watch out for this

Using this method with fewer than three qualifying children. Only filers with three or more qualifying children on line 16 can use the Social Security tax method. Filers with one or two children skip this line entirely and use only the 15% earned income method from line 20.

Related lines on your return

• Line 20 — Schedule 8812 — 15% earned income method; compared against this alternative
• Line 22 — Schedule 8812 — Larger of line 20 or line 21; the better result is used
• Line 27a — Form 1040 — Earned income credit; subtracted in this calculation