11.3 Credits, Payments, and AMT Concepts
Key Takeaways
- REG Area IV covers computing tax liability from taxable income, distinguishing refundable from nonrefundable credits, estimated-tax safe harbors, the net investment income tax, and the alternative minimum tax at a concept level.
- A nonrefundable credit reduces tax only to zero (or to a stated floor); a refundable credit can exceed tax and generate or increase a refund.
- Payments such as withholding, estimated payments, and extension payments are applied AFTER total tax is computed and behave like refundable items.
- The 3.8% net investment income tax (NIIT) applies to the lesser of net investment income or modified AGI over $200,000 (single) / $250,000 (MFJ); these thresholds are not indexed.
- The 2026 AMT exemption is $90,100 (single) and $140,200 (MFJ), phasing out at 50 cents per dollar of AMTI above $500,000 / $1,000,000; AMT is a parallel tax, not a deduction, payment, or credit.
From Taxable Income to Refund or Balance Due
Once taxable income is set, REG shifts from income classification to liability reconciliation. The 2026 blueprint includes calculating regular tax from taxable income, distinguishing refundable from nonrefundable credits, recalling individual estimated-tax safe harbor rules, and applying the net investment income tax (NIIT) and alternative minimum tax (AMT) when the facts require it.
Tax, Credits, Other Taxes, Payments
Keep the order straight, because it is the single most-tested mechanic in the area. Taxable income produces regular income tax; credits reduce that tax; other taxes increase total tax; and payments reduce the amount due after total tax is known. Many wrong answers come from using withholding as if it were a credit, or treating a nonrefundable credit as if it could by itself create a refund.
| Item | Return role | Effect |
|---|---|---|
| Regular income tax | Tax computation | Begins liability after taxable income |
| Nonrefundable credit | Credit | Reduces tax only to zero (no refund of the excess) |
| Refundable credit | Credit / payment-like | Can exceed tax and increase the refund |
| Withholding (W-2/1099) | Payment | Applied after total tax; refundable if it exceeds tax |
| Estimated tax payment | Payment | Reduces balance due; supports safe-harbor analysis |
| Net investment income tax | Other tax | Adds 3.8% when MAGI exceeds the threshold |
| AMT | Other tax | Adds the excess of tentative minimum tax over regular tax |
Refundable Versus Nonrefundable
A nonrefundable credit is valuable only to the extent it reduces the relevant tax; once tax hits zero, the unused amount disappears unless a specific carryforward or refundable portion is provided (the foreign tax credit carries back one year and forward ten; the child tax credit has a partially refundable additional child tax credit). A refundable credit (such as the earned income tax credit and the premium tax credit) can exceed tax and increase the refund. REG often asks for the final balance due, so classify each credit before doing arithmetic.
Read whether the question labels a credit refundable, nonrefundable, limited, carried forward, or partially refundable.
Estimated Tax and Safe Harbors
Individuals must make estimated payments when withholding is insufficient. The general safe harbor avoids the underpayment penalty if total timely payments equal the lesser of 90% of the current-year tax or 100% of the prior-year tax (110% if prior-year AGI exceeded $150,000, or $75,000 MFS). The exam supplies prior-year tax, current-year tax, withholding, and payment timing; your task is to decide whether the penalty is avoided or an additional payment is required. There is also a de-minimis rule: no penalty applies when the balance due after withholding is less than $1,000.
Net Investment Income Tax
The NIIT is a 3.8% surtax on the lesser of net investment income or the excess of modified AGI (MAGI) over the threshold. The thresholds are $200,000 (single/HoH), $250,000 (MFJ), and $125,000 (MFS) and are not indexed for inflation, so more taxpayers cross them each year. Net investment income includes interest, dividends, capital gains, rents, royalties, and passive income, but not wages or active business income.
AMT Concept Map
The alternative minimum tax (AMT) is a parallel system that starts with regular taxable income, adds back preference and adjustment items (the standard deduction, certain state and local taxes, private-activity-bond interest, the bargain element on incentive stock options), subtracts an exemption, and applies AMT rates (26% / 28%) to alternative minimum taxable income (AMTI). For 2026 the exemption is $90,100 (single) and $140,200 (MFJ), and it phases out at 50 cents per dollar of AMTI above $500,000 (single) and $1,000,000 (MFJ) -- a steeper, lower phaseout than prior years.
AMT equals the excess of tentative minimum tax over regular tax; it is not a deduction, payment, or refundable credit.
Deeper AMT computation lives in the Tax Compliance and Planning (TCP) discipline, but REG candidates need the concept because Form 1040 review shows AMT on the tax side of the return. If a simulation supplies AMTI, the exemption, tentative minimum tax, and regular tax, compute the comparison as instructed. A worked example: a single taxpayer with AMTI of $300,000 takes the full $90,100 exemption (no phaseout below $500,000), leaving $209,900 taxed at 26% up to the bracket breakpoint -- the resulting tentative minimum tax is compared with regular tax, and only the excess is the AMT add-on.
If regular tax already exceeds tentative minimum tax, AMT is zero.
CPA Exam Workflow
- Compute regular tax from taxable income using the supplied rate schedule.
- Apply nonrefundable credits within their limits (drive tax toward zero, no refund of the excess).
- Add other taxes -- NIIT, AMT, additional Medicare tax, or the 10% early-distribution penalty -- when the facts trigger them.
- Subtract withholding, estimated payments, extension payments, and refundable credits.
- Determine the refund, balance due, or estimated-tax penalty exposure.
The most common scoring loss in this area is mixing up the order: applying a payment as a credit, applying a nonrefundable credit against NIIT or AMT it cannot offset, or netting an other-tax before credits. Lock the sequence -- tax, then credits, then other taxes, then payments -- and most balance-due simulations resolve to a single clean number. Because credits and payments depend on AGI, filing status, and dependents from the prior sections, an error upstream surfaces here as a wrong refund, which is why TBS graders favor this reconciliation.
A taxpayer has regular income tax of $2,400 before credits, a $3,000 nonrefundable credit with no carryforward, and $900 of federal withholding. What is the resulting refund or amount due from these items?
A single taxpayer has modified AGI of $260,000, including $50,000 of net investment income. To how much of an amount does the 3.8% net investment income tax apply?