How Income Tax Is Computed: Brackets, Allowances, Credits & Effective Rates

What you'll build

What you will be able to do

Each lab ends with a concrete result that you build yourself and the checker confirms, cell by cell.

• Split Theo's taxable income of 64,500 across five brackets, tax each slice, add the slices up and confirm the total with a one-cell SUMPRODUCT rate-step formula.
• Calculate Nadia's tax, net income and three different tax rates before and after a 3,000 raise that pushes her into the 40% bracket, and prove that she still keeps more money.
• Walk Lena's return down the taxable-income chain: adjusted income, a medical floor with MAX, a capped deduction with MIN, itemised vs standard deduction with MAX and the final taxable income.
• Shrink the personal allowance for five clients above 100,000, tax what is left, find the hidden 60% marginal rate inside the taper zone and the income where the allowance is gone.
• Look up each client's standard deduction and bracket thresholds by filing status, calculate the tax for five returns and measure what Ava and Ben save by filing jointly.
• Apply non-refundable and refundable credits for five clients, find the final tax (which can be negative), turn it into a refund or balance due and total the credit that was lost.
• Run the whole calculation for twelve incomes from 10,000 to 250,000 and chart how the effective rate climbs smoothly while the marginal rate jumps in steps.
• Build Ravi's complete summary in one column: gross, adjusted and taxable income, tax before and after credits, net income, refund or balance due and the effective rate, then prove it with check cells.