CPA REG · INDIVIDUAL FEDERAL TAX · 2025

Form 1040 Tax Lab

Edit the facts. Trace every dollar from gross income to tax after credits.

2025 assumptionsOrdinary income modelEditable thresholds

1 · Income

Generally included unless excluded

WagesInterestDividendsBusiness incomeRental incomeOther taxable income

Enter taxable amounts only. Municipal bond interest, gifts, inheritances, and qualifying life-insurance proceeds are excluded here.

2 · Above-the-line adjustments

Deductible IRAHSA deductionStudent-loan interest½ self-employment taxSelf-employed health insuranceOther valid adjustments

These reduce AGI whether the taxpayer itemizes. Assume all entered amounts satisfy limits.

3 · Filing status & deductions

Filing status

Medical deduction allowedState/local taxes allowedHome mortgage interestCharitable contributionsOther itemized deductionsExtra deduction amount

Enter deductible amounts after floors, ceilings, and classification rules. The calculator chooses the larger permitted deduction.

4 · Credits

Nonrefundable creditsRefundable credits

Nonrefundable credits cannot reduce regular tax below $0. Refundable credits may.

LIVE COMPUTATION

Tax waterfall

Scope: simplified federal regular tax on ordinary income. It excludes preferential capital-gain rates, QBI, self-employment tax, AMT, NIIT, phaseouts, dependents, payments, and most special limitations.

Computation ladder

Marginal brackets

Each rate applies only to income inside that layer—not to all taxable income.

Exam method: fill each bracket from the bottom up, then add the tax from every occupied layer.

What each line means

Gross income

All income from whatever source unless the IRC excludes it. Classification comes before arithmetic.

Adjustments → AGI

Above-the-line deductions reduce AGI. They can matter again when another deduction or credit uses AGI as a limit.

Itemized deductions

Personal deductions below AGI. Use the allowed amount after floors and caps; compare the total with the standard deduction.

Taxable income

AGI minus the chosen deduction, floored at $0 in this model.

Credits

Credits reduce tax dollar-for-dollar. Deductions only reduce the base on which tax is computed.

High-yield classification

IncludeWages, taxable interest, business income, rents, prizes, gambling winnings, unemployment compensationGI

ExcludeGifts, inheritances, municipal bond interest, qualifying life-insurance proceeds, return of capital to basisNo GI

AdjustmentDeductible IRA, HSA, ½ SE tax, qualifying student-loan interest, self-employed health insuranceTo AGI

ItemizedAllowed medical, taxes, interest, charity, and other permitted Schedule A amountsFrom AGI

Trap: tax-exempt income may still appear in facts. Do not force every receipt into gross income.

Editable tax-year assumptions

Tax-year labelRates, comma-separated (%)

Bracket ceilings

Enter the upper taxable-income ceiling for the first 6 brackets. The 7th rate applies above the last ceiling.

SingleMarried filing jointlyMarried filing separatelyHead of household

Defaults reflect 2025 federal ordinary-income brackets and basic standard deductions. Editing them changes the live model; verify the tax year assigned by the exam question.

REG CLASSIFICATION DRILL

0 / 0

Choose the best treatment.

Three-bucket attack

Inclusion?

Start with broad gross income, then search for a specific exclusion.

Where deducted?

Classify as business expense, adjustment to income, itemized deduction, or nondeductible personal expense.

Any limit?

Only after classification should you apply AGI floors, caps, basis, or phaseouts.

Memory hook: I-W-L — Inclusion, Where, Limit.

Individual Income Tax Walkthrough Calculator