Guides
21 explainers on the calculations behind the OzCalc tools — written out in full, with the formulas, the thresholds and the traps.
A calculator gives you a number. It does not tell you why the number is what it is, which is usually what you actually needed to know. These guides do that part: where each rule comes from, which figure applies for the current financial year, and the specific misconceptions that lead people to the wrong answer.
Every guide names its sources and the date it was last reviewed. Where a figure is set by the ATO, Fair Work or a state authority, we link to that source rather than asking you to take our word for it. None of it is personal advice — it is the arithmetic, explained well enough that you can check it yourself. If something here looks wrong, tell us and we will correct it.
Pay and super
What an advertised salary becomes after tax, how employer superannuation sits alongside it, and how hourly rates and leave hours convert.
- How Australian take-home pay is actually calculatedFollow a $95,000 salary from gross to bank account: PAYG withholding on each pay, year-end income tax, the low income tax offset and the Medicare levy.8 min read · reviewed 7 September 2026
- Salary plus super versus a total packageTwo job ads can quote the same number and pay thousands apart. How to tell which one includes superannuation, and how to compare them properly.7 min read · reviewed 7 September 2026
- The superannuation guarantee, explainedWhat your employer must contribute in 2026–27, which earnings it applies to, when it has to be paid, and what the maximum contribution base does to high salaries.7 min read · reviewed 7 September 2026
- Converting an hourly or casual rate into an annual salaryThe 38-hour week, 52-week year and casual loading that decide whether a quoted hourly rate matches the salary in the next job ad.8 min read · reviewed 7 September 2026
- How annual leave is accrued and converted in AustraliaFour weeks, 152 hours and a 7.6-hour day: how leave accrues under the NES, why payslips store hours, and what leave loading actually adds.8 min read · reviewed 7 September 2026
Tax and levies
Income tax brackets, GST, the Medicare levy and study loan repayments, using the current ATO figures.
- Australian income tax brackets for 2026–27The resident rates, what a marginal rate does and does not mean, and why moving into a higher bracket never reduces your take-home pay.8 min read · reviewed 7 September 2026
- How GST works in AustraliaAdding GST is ten per cent; removing it is one eleventh. Why the two are different, plus GST-free items, invoices and rounding.7 min read · reviewed 7 September 2026
- The Medicare levy and the Medicare levy surchargeTwo separate charges that are often confused. Who pays the 2% levy, who pays the surcharge on top, and when private hospital cover costs less than the surcharge.8 min read · reviewed 7 September 2026
- How HELP and HECS repayments come out of your payRepayment thresholds for 2026–27, why the rate applies to income above a threshold rather than all of it, indexation, and the refund surprise at tax time.8 min read · reviewed 7 September 2026
- How PAYG withholding is calculated on an Australian payslipThe ATO formula your employer actually uses, why each pay is rounded, and why a correct payslip still does not match your year-end tax bill.9 min read · reviewed 7 September 2026
- The Australian financial year, and why 1 July mattersWhy the income year runs from 1 July to 30 June, which year a date belongs to, and what actually changes at EOFY besides a new tax scale.7 min read · reviewed 7 September 2026
Home and property
The arithmetic behind a mortgage and a rental ledger, including the parts that surprise first-time buyers and renters.
- House deposits, LVR and why 20 percent still mattersHow a deposit becomes a loan-to-value ratio, when lenders charge mortgage insurance, and why a 5% deposit is not one-quarter of a 20% one in cost.9 min read · reviewed 7 September 2026
- How mortgage interest is charged and repaidWhy the first years of a loan are mostly interest, what an extra $100 a month really saves, and how an offset account compares to a redraw.9 min read · reviewed 7 September 2026
- Why monthly rent is not weekly rent times fourAustralian rent is advertised weekly and often charged monthly. The 52-week year explains the shortfall that catches out new renters every year.7 min read · reviewed 7 September 2026
Saving and interest
How compounding actually accumulates, and why the frequency matters more than people expect.
- How credit card interest is charged in AustraliaDaily compounding, the interest-free period, cash advances, and why paying only the minimum leaves a balance growing for years.8 min read · reviewed 7 September 2026
- Compound interest, and why frequency mattersThe difference between simple and compound interest, what daily versus monthly compounding is worth, and how regular deposits change the maths.8 min read · reviewed 7 September 2026
Household bills
Turning appliance labels, energy bills and everyday pricing — markup, margin and discounts — into costs you can act on.
- Markup versus margin, and why they are never the same numberA 25% markup is a 20% margin. How Australian small businesses mix the two up, and how GST sitting on top changes the cash in the till.8 min read · reviewed 7 September 2026
- Working out what an appliance costs to runWatts, kilowatt-hours and cents per kWh, plus why the daily supply charge does not belong in the cost of boiling a kettle.7 min read · reviewed 7 September 2026
Dates and working days
Counting business days and public holidays the way contracts, notice periods and payroll do.
- How business days are counted in AustraliaInclusive counts, weekends, state public holidays and the difference between counting between two dates and adding days to one.7 min read · reviewed 7 September 2026
- Australian public holidays, state by stateWhich holidays are national, which are local, how substitute days work when a holiday falls on a weekend, and why Easter moves each year.8 min read · reviewed 7 September 2026
Driving and travel
Reading Australian fuel consumption figures and costing a drive before you leave.
How these guides are written
Each guide is written against the same dataset the calculators use, so a threshold quoted in an article and a threshold used in a result cannot drift apart. When the ATO updates a figure, the data file changes and both follow. Our editorial policy sets out how that review works and how we handle corrections.