TL;DR
- The Child Tax Credit phases out at a fixed rate: $50 is subtracted for every $1,000 (or fraction) of Modified Adjusted Gross Income above the threshold for a given filing status. - For 2026, the phase-out threshold is $200,000 MAGI for single and Head of Household filers, or $400,000 for Married Filing Jointly, under the One Big Beautiful Bill Act. - The maximum credit modeled is $2,200 per qualifying child under 17, plus $500 per other dependent through the nonrefundable Credit for Other Dependents. - Up to $1,700 of the per-child credit is refundable through the Additional Child Tax Credit, but that refundable amount is separately capped at 15% of earned income above $2,500. - A family with two qualifying children does not lose credit eligibility until MAGI reaches roughly $488,000 (MFJ), because the phase-out reduces the credit gradually rather than eliminating it at the threshold itself.
The Child Tax Credit is often described by its headline number, but the figure that actually lands on a tax return depends on a phase-out calculation that most filers never see modeled directly. Two variables determine the outcome: how many qualifying children and other dependents are being claimed, and how far Modified Adjusted Gross Income sits above the threshold for the filer's status. Because the phase-out is linear and applies in discrete steps rather than smoothly, the same income increase can produce a noticeably different credit reduction depending on exactly where a household's MAGI falls relative to the nearest $1,000 increment.
Informational calculation reference only. All equations, tools, and outputs on this page are intended strictly for educational modeling and mathematical illustration. They do not constitute certified financial, legal, or tax advice. For specific scenarios, consult a certified public accountant (CPA) or a fiduciary financial advisor.
The mathematical formula behind the calculation
The calculation begins with the gross credit, which sums the per-child and per-dependent amounts before any income-based reduction is applied:
$$ GrossCredit = (Children \times \$2{,}200) + (OtherDependents \times \$500) $$
Once gross credit is established, the phase-out formula determines how much of it survives the MAGI test. The reduction is calculated in $1,000 increments above the threshold, rounding any partial increment up to the next full $1,000, then multiplying by a flat $50 reduction per increment:
$$ PhaseOut = \left\lceil \frac{MAGI - Threshold}{\$1{,}000} \right\rceil \times \$50 $$
The threshold itself depends on filing status: $200,000 for single and Head of Household filers, and $400,000 for Married Filing Jointly. Because the formula rounds up rather than prorating smoothly, even $1 of MAGI above the threshold triggers a full $50 reduction, and the reduction increases by another $50 with every additional $1,000 increment crossed.
The net nonrefundable credit is whichever is greater of zero or the gross credit minus the phase-out:
NetCredit = \max(0,\ GrossCredit - PhaseOut)
A separate calculation then determines how much of that net credit can be refunded as the Additional Child Tax Credit, rather than only offsetting tax owed. The refundable amount is the smallest of three limits: the remaining credit itself, a per-child cap of $1,700, or 15% of earned income above a $2,500 floor:
$$ RefundableACTC = \min\Big(RemainingCredit,\ Children \times \$1{,}700,\ 0.15 \times (EarnedIncome - \$2{,}500)\Big) $$
That third limit is what separates the Child Tax Credit's refundable design from a simple dollar-for-dollar tax offset — a household with little or no earned income cannot receive the full refundable amount even if their tax liability is zero, because the earned-income test caps how much refund the formula allows.
Step-by-step practical calculation example
Consider a married couple filing jointly with two qualifying children under 17, no other dependents, and a MAGI of $430,000.
Step 1: Calculate the gross credit. Two children at $2,200 each produces a gross credit of $4,400, with no Credit for Other Dependents in this scenario.
Step 2: Calculate the excess over the threshold. MFJ threshold is $400,000, so MAGI exceeds it by $430,000 − $400,000 = $30,000.
Step 3: Convert the excess into $1,000 increments. $30,000 ÷ $1,000 = 30 exactly, so no rounding up is needed in this case: 30 full increments.
Step 4: Apply the $50 per-increment reduction. 30 increments × $50 = $1,500 in phase-out.
$$ PhaseOut = \left\lceil \frac{430{,}000 - 400{,}000}{1{,}000} \right\rceil \times 50 = 30 \times 50 = \$1{,}500 $$
Step 5: Subtract the phase-out from the gross credit. $4,400 − $1,500 = $2,900 net credit.
Step 6: Compare against tax liability. If this household's federal tax liability before credits is $18,000, the entire $2,900 reduces that liability dollar-for-dollar and none of it needs the refundable ACTC calculation, since there is ample tax owed to absorb the full nonrefundable credit.
| Variable | Value in this example |
|---|---|
| Qualifying children | 2 |
| Filing status | Married Filing Jointly |
| MAGI | $430,000 |
| Threshold | $400,000 |
| Excess over threshold | $30,000 |
| $1,000 increments (rounded up) | 30 |
| Phase-out reduction | $1,500 |
| Gross credit | $4,400 |
| Net credit after phase-out | $2,900 |
Strategic applications for financial modeling
MAGI threshold proximity planning. Because the phase-out begins at a hard dollar threshold rather than phasing in gradually beforehand, modeling a household's MAGI trajectory relative to the $200,000 or $400,000 line before year-end can clarify whether a retirement account contribution, HSA contribution, or timing shift on realized capital gains would meaningfully change the credit outcome by keeping MAGI under a key increment.
Full phase-out point estimation. Setting NetCredit to zero and solving for MAGI shows the income level at which a family's credit disappears entirely. For a two-child MFJ household, gross credit of $4,400 divided by $50 per increment implies 88 increments, or $88,000 of excess MAGI, placing full phase-out around $488,000 — a useful benchmark for high-earning households modeling multi-year income projections.
Multi-child sensitivity modeling. Because gross credit scales linearly with the number of qualifying children while the phase-out formula does not depend on child count at all, adding a child to the household model increases both the gross credit and the MAGI level at which the credit fully phases out, without changing the phase-out rate itself.
ACTC eligibility modeling for variable-income households. Self-employed filers or households with fluctuating earned income benefit from modeling the 15%-of-earned-income limit in years when income dips, since a low-earned-income year can cap the refundable portion well below the $1,700-per-child ceiling even when the nonrefundable credit calculation alone would suggest a larger benefit.
Common pitfalls and variable mistakes
Using AGI instead of MAGI. For the large majority of filers, Modified AGI for this calculation equals AGI, but certain add-backs (such as excluded foreign earned income) can create a gap. Modeling with AGI when a MAGI add-back applies understates the phase-out.
Forgetting the rounding-up rule. Treating the phase-out as a smooth percentage rather than rounding each partial $1,000 increment up to a full increment slightly understates the reduction in every case where the excess isn't an exact multiple of $1,000.
Applying the wrong threshold for filing status. Modeling a Head of Household filer against the $400,000 MFJ threshold, or vice versa, produces a materially incorrect phase-out figure, since HOH filers use the same $200,000 threshold as single filers.
Confusing the $500 Credit for Other Dependents with the full $2,200 credit. Dependents who don't meet the under-17, valid Social Security Number test — including 17-year-olds and qualifying relatives — fall under the $500 nonrefundable ODC, not the larger CTC, even though both share the same phase-out mechanics.
Ignoring the earned-income cap on the ACTC. Assuming the full $1,700-per-child refundable amount is available regardless of income overstates the refund for lower-earned-income households, since the 15%-of-earned-income-above-$2,500 test can bind before the per-child cap does.
Modeling the Child Tax Credit with the formulas above turns a single headline number into a household-specific figure that accounts for filing status, dependent count, and where MAGI falls relative to the phase-out threshold. The Child Tax Credit Calculator applies this same phase-out and ACTC logic automatically across filing statuses and dependent counts.
Disclaimer: While we strive for absolute mathematical precision, actual real-world financial outcomes may vary based on institutional fees, localized tax brackets, changes in federal legislation, or fluctuating market indexes.