Mathematics Standard • Year 11 • Module 3 • Lesson 8
Calculating Income Tax
Apply the 2024–25 tax brackets, Medicare levy, and PAYG reconciliation to realistic Australian taxpayer scenarios.
Reference — 2024–25 ATO tax brackets (residents)
| Taxable income | Tax on this income |
|---|---|
| $0 – $18,200 | Nil |
| $18,201 – $45,000 | Nil + 19c for each $1 over $18,200 |
| $45,001 – $120,000 | $5,092 + 32.5c for each $1 over $45,000 |
| $120,001 – $180,000 | $29,467 + 37c for each $1 over $120,000 |
| $180,001 + | $51,667 + 45c for each $1 over $180,000 |
Medicare levy = 2% of taxable income (added separately to income tax).
Problem 1 — Refund for a graduate teacher
Mia is a first-year graduate teacher. Her taxable income for the year was $74,200. Her employer withheld $16,250 in PAYG tax across the year.
Set up: What are we solving for?
(i) Calculate Mia's income tax using the bracket formula. 2 marks
(ii) Calculate Mia's Medicare levy and total tax liability. 2 marks
(iii) Determine whether Mia receives a refund or owes a debt, and state the amount. 1 mark
Stuck? Compare PAYG withheld with the total liability (income tax + Medicare levy), not income tax alone.Problem 2 — Plumber with a tax debt
Riley is a self-employed plumber. He earned $108,400 in gross fees and $720 in bank interest. His allowable deductions total $4,260. Riley does not have PAYG withheld; instead he made quarterly PAYG instalments totalling $22,400.
Set up: What are we solving for?
(i) Calculate Riley's taxable income. 1 mark
(ii) Calculate Riley's income tax, Medicare levy and total tax liability. 3 marks
(iii) Compare the PAYG instalments with the total liability and state whether Riley receives a refund or owes a debt — and by how much. 2 marks
Stuck? Apply the brackets to taxable income, not to gross fees. The deductions reduce the taxable amount first.Problem 3 — Top bracket — a senior engineer
Dr Patel is a senior engineer with a taxable income of $192,400. Her employer withheld $59,800 in PAYG tax over the year.
Set up: What are we solving for?
(i) Identify the correct bracket and calculate Dr Patel's income tax. 2 marks
(ii) Calculate Medicare levy and total tax liability. 2 marks
(iii) Calculate Dr Patel's effective tax rate (total liability ÷ taxable income × 100), and briefly explain why this is lower than the 45% marginal rate. 2 marks
Stuck? Effective rate < marginal rate because only the income above the threshold is taxed at the top rate — the lower portions are taxed at lower rates.Problem 4 — Bracket boundary — promoted mid-year
Sami had a taxable income of $45,000 last financial year — exactly at the bracket boundary. After a promotion this year, his taxable income is $48,800. His PAYG withheld this year was $8,600.
Set up: What are we solving for?
(i) Calculate Sami's total tax liability (income tax + Medicare levy) on his $48,800 taxable income this year. 2 marks
(ii) Determine whether he receives a refund or owes a debt and state the amount. 1 mark
(iii) Sami's promotion added $3,800 to his taxable income this year (compared with $45,000 last year). Calculate the extra tax (income tax only) on that additional $3,800, and explain in one sentence why the marginal rate of 32.5% applies to the whole $3,800. 2 marks
Stuck on (iii)? At $45,000 last year, he was right at the threshold. Every extra dollar this year sits above $45,000, so it all attracts the 32.5% rate.Problem 5 — Comparing two job offers (after tax)
Priya is choosing between two job offers. She wants to know which leaves her with more after-tax income (taxable income minus total tax liability), so she can compare like with like.
Job A: Taxable income of $78,400 per year.
Job B: Taxable income of $86,200 per year.
Set up: What are we solving for?
(i) Calculate Job A's total tax liability and after-tax income. 2 marks
(ii) Calculate Job B's total tax liability and after-tax income. 2 marks
(iii) By how much more does Job B leave Priya after tax compared with Job A? State a clear conclusion sentence. 2 marks
Stuck? After-tax income = taxable income − total tax liability. Calculate one job fully, then repeat for the other before comparing.How did this worksheet feel?
What I'll revisit before next class:
Problem 1 — Mia's refund
Set up. Identify Mia's bracket, calculate income tax and Medicare levy, sum to total liability, then compare against PAYG.
(i) $74,200 in $45,001 – $120,000 bracket. Income tax = $5,092 + 0.325 × ($74,200 − $45,000) = $5,092 + 0.325 × $29,200 = $5,092 + $9,490 = $14,582.00.
(ii) Medicare = $74,200 × 0.02 = $1,484. Total liability = $14,582 + $1,484 = $16,066.00.
(iii) PAYG $16,250 > liability $16,066 → refund of $184.00.
Problem 2 — Riley's tax debt
Set up. Gross income minus deductions gives taxable income; apply brackets and Medicare; reconcile against PAYG instalments.
(i) Gross = $108,400 + $720 = $109,120. Taxable income = $109,120 − $4,260 = $104,860.
(ii) $104,860 in $45,001 – $120,000 bracket. Income tax = $5,092 + 0.325 × ($104,860 − $45,000) = $5,092 + 0.325 × $59,860 = $5,092 + $19,454.50 = $24,546.50. Medicare = $104,860 × 0.02 = $2,097.20. Total liability = $26,643.70.
(iii) PAYG $22,400 < liability $26,643.70 → tax debt of $4,243.70. (Conclusion sentence essential for the second mark.)
Problem 3 — Dr Patel, top bracket
Set up. $192,400 is in the top bracket — apply base + 45% on the excess above $180,000.
(i) $192,400 in $180,001+ bracket. Income tax = $51,667 + 0.45 × ($192,400 − $180,000) = $51,667 + 0.45 × $12,400 = $51,667 + $5,580 = $57,247.00.
(ii) Medicare = $192,400 × 0.02 = $3,848. Total liability = $57,247 + $3,848 = $61,095.00.
(iii) Effective rate = $61,095 ÷ $192,400 × 100 ≈ 31.8%. This is lower than 45% because the 45% rate only applies to the $12,400 of income above $180,000 — the lower portions are taxed at 0%, 19%, 32.5% and 37% respectively, dragging the average down.
Problem 4 — Sami's promotion at the bracket boundary
Set up. Calculate this year's liability, reconcile, then isolate the marginal effect of the extra $3,800.
(i) $48,800 in $45,001 – $120,000 bracket. Income tax = $5,092 + 0.325 × ($48,800 − $45,000) = $5,092 + 0.325 × $3,800 = $5,092 + $1,235 = $6,327. Medicare = $48,800 × 0.02 = $976. Total liability = $7,303.00.
(ii) PAYG $8,600 > liability $7,303 → refund of $1,297.00.
(iii) Extra income tax on the $3,800 = 0.325 × $3,800 = $1,235.00. The entire $3,800 sits above the $45,000 threshold, so every dollar is taxed at the 32.5% marginal rate — none of it is at the lower 19% rate.
Problem 5 — Comparing two jobs after tax
Set up. Compute total liability for each job, subtract from taxable income to get after-tax income, then compare.
(i) Job A ($78,400). Income tax = $5,092 + 0.325 × ($78,400 − $45,000) = $5,092 + 0.325 × $33,400 = $5,092 + $10,855 = $15,947. Medicare = $78,400 × 0.02 = $1,568. Total liability = $17,515. After-tax income = $78,400 − $17,515 = $60,885.00.
(ii) Job B ($86,200). Income tax = $5,092 + 0.325 × ($86,200 − $45,000) = $5,092 + 0.325 × $41,200 = $5,092 + $13,390 = $18,482. Medicare = $86,200 × 0.02 = $1,724. Total liability = $20,206. After-tax income = $86,200 − $20,206 = $65,994.00.
(iii) Difference = $65,994 − $60,885 = $5,109. Job B leaves Priya $5,109.00 better off after tax per year. (The extra $7,800 of taxable income generates only $5,109 of extra after-tax income because the additional dollars are all taxed at 32.5% income tax + 2% Medicare = 34.5%.)