How the credit is calculated
The Child Tax Credit is calculated in two stages. First, the IRS works out your total CTC: $2,200 for each qualifying child, reduced if your income is over the phase-out threshold. Second, it splits that total into a nonrefundable part (which can only cancel tax you owe) and a refundable part, the ACTC (which can come back as cash). The ACTC has its own formula, and it is the formula most families get wrong.
- Stage 1: $2,200 × qualifying children, minus $50 per $1,000 (or fraction) of MAGI above $200,000 ($400,000 joint).
- Stage 2: the ACTC equals 15% of earned income above $2,500, capped at $1,700 per qualifying child.
- The refund can never exceed the ACTC cap, and the nonrefundable $500 remainder needs tax liability.
- Schedule 8812 does this arithmetic for you — but understanding it catches errors before you file.
The ACTC formula, worked twice
The refundable amount is 15% of your earned income above $2,500, capped at $1,700 per qualifying child. Earned income means wages, salaries, and net self-employment earnings — not interest, dividends, or other passive income.
Example 1 — below the cap. A single parent with one qualifying child, no tax liability, and $12,500 of earned income. 15% × ($12,500 − $2,500) = 15% × $10,000 = $1,500. The refund is $1,500. The remaining $700 of the $2,200 credit is unused: $200 of it is above the ACTC formula result, and $500 of it is the nonrefundable remainder that needs tax liability.
Example 2 — at the cap. A married couple with one qualifying child, no tax liability, and $20,000 of earned income. 15% × ($20,000 − $2,500) = 15% × $17,500 = $2,625 — but the ACTC caps at $1,700 per child, so the refund is $1,700. The remaining $500 is unused without tax liability. Earning more does not raise the refund past the cap.
Families with three or more qualifying children have an alternative ACTC formula based on Social Security taxes paid minus any Earned Income Tax Credit, and can use whichever result is larger. Schedule 8812 tests both formulas; most families with fewer than three children never meet the alternative.
The phase-out slope, worked once
Before the split, the total credit shrinks if your MAGI is over the threshold. A married couple filing jointly with two qualifying children and MAGI of $410,000: excess $10,000, reduction $50 × 10 = $500, total CTC $4,400 − $500 = $3,900. If that couple owed $3,900 or more in tax, the whole $3,900 offsets tax and there is no ACTC question. If they owed nothing, the ACTC formula (based on earned income) decides how much of the $3,900 comes back as cash, capped at $1,700 per child — $3,400 for two children — and the rest is unused.
How Schedule 8812 does it
Schedule 8812, attached to Form 1040 or 1040-SR, walks through the calculation line by line: it lists each qualifying child and each other dependent, applies the phase-out, computes the ACTC from earned income, and separates the nonrefundable CTC from the refundable ACTC. Tax software and the IRS Free File programs complete it automatically from your answers, but the lines are worth reading once: most CTC errors are a wrong child count, a wrong SSN, or a phase-out misread, and all three show up on this schedule before the return is filed.
Sources to check: IRS Schedule 8812 and instructions; IRS, Child Tax Credit (irs.gov); IRS Taxpayer Advocate Service, Claiming the Child Tax Credit or Credit for Other Dependents.