An explanation of the formulas, data sources, and update process behind every calculator on this site.
This page sets out where our figures come from, how each category of calculator works, and what its results can and cannot tell you. For how content is written, reviewed and corrected, see our editorial policy.
| Source | What we take from it | Typical update |
|---|---|---|
| Australian Taxation Office | Income tax rates and thresholds, Medicare levy, LITO, HECS-HELP, super caps, FBT, CGT, depreciation | 1 July, plus announced changes |
| Services Australia | Age Pension rates, income and assets tests, deeming rates | March and September |
| Reserve Bank of Australia | Cash rate and official rate history | Board meeting decisions |
| State revenue offices | Stamp duty rates, first home buyer concessions, land tax | State budgets |
| Australian Bureau of Statistics | Average heights, CPI, population and national accounts | Per publication schedule |
| Fair Work Ombudsman | Hours of work and record-keeping requirements | As amended |
| Standards Australia and the NCC | Building and electrical reference values | As amended |
Where a figure is a typical value rather than a published rate — ingredient densities, material weights, fuel consumption — we say so on the page. Those are useful starting points, not constants, and the page explains what shifts them.
These use the current financial year's ATO rates, including the Medicare levy, the low income tax offset and the relevant HECS-HELP repayment thresholds. Superannuation calculators use current contribution caps.
What they cannot do is account for your full circumstances. Offsets you may be entitled to, deductions, salary sacrifice arrangements, private health cover status and family income tests all change the outcome. A tax calculator gives you a well-founded estimate of the general case, which is genuinely useful for planning and is not a substitute for your actual return.
Repayment figures use standard amortisation — the same formula lenders use to split each payment between principal and interest. Stamp duty calculators use each state and territory's published duty scales and first home buyer thresholds, which differ substantially between jurisdictions.
Interest rates shown as defaults are illustrative only. Your actual rate depends on your lender, loan type, deposit size and credit assessment, and will differ from any example. Lender fees, lenders mortgage insurance and offset arrangements are not included unless a calculator states otherwise.
Health calculators use named, published equations — the Mifflin-St Jeor equation for basal metabolic rate, for example — rather than unattributed formulas. Where a formula has known limitations, the page says so.
BMI is the clearest example. It was designed to describe populations, not individuals, and it does not distinguish muscle from fat or account for build. A muscular person can register as overweight on BMI while being nothing of the sort. We publish the calculation because it is widely used and people need to understand it, and we explain its limits on the same page rather than presenting a number as a verdict. Health calculators here are educational tools. They do not diagnose anything, and they are not a substitute for seeing a doctor.
Unit conversions use exact defined factors wherever one exists — an inch is exactly 2.54 centimetres, a pound is exactly 0.45359237 kilograms. These are definitions rather than measurements, so the conversion is exact and the only question is rounding.
Where a conversion depends on a standard that differs by country, the calculator names which one it is using. Cup sizes, tablespoon sizes and fluid ounces all vary, and a tool that silently applies the American value will be wrong for an Australian recipe. Volume-to-weight conversions additionally depend on density, which is why those calculators ask what you are measuring.
We round displayed results to a sensible number of decimal places for the quantity being measured, and calculate at full precision internally so that rounding does not accumulate through a multi-step calculation.
Two consequences worth knowing. A result may differ in the last decimal place from another tool that rounds at each step — ours is generally the more accurate. And a calculator will never show more precision than its inputs support, because a mean of 4.2857143 derived from seven whole numbers implies an accuracy that does not exist.
Before a calculator is published, its logic is tested against worked examples with independently known answers. Testing specifically covers the cases that break calculators in practice: zero and blank inputs, negative values where they are impossible, division by zero, values at the boundary between tax brackets or grade bands, and inputs far outside the expected range.
Where a calculator cannot give a meaningful answer, it says so rather than returning a plausible-looking number. A target that cannot be reached is reported as unreachable, not as a percentage above 100.
Why does your result differ from another calculator?
Usually assumptions rather than arithmetic. Different tools apply different rounding, different unit standards, or different default values. Our pages state the assumptions they use, so you can check which one matches your situation.
Can I use these figures for my tax return?
They are a reasonable estimate for planning, not a return. Your actual position depends on deductions, offsets and circumstances no general calculator can know. Use the ATO's own tools or a registered tax agent for lodgement.
How often are the rates updated?
Tax and super figures are reviewed for each financial year from 1 July, and when changes are announced. Centrelink rates change in March and September. Each page shows its review date.
Why does a calculator sometimes refuse to give an answer?
Because the honest answer is that there isn't one. If your inputs make a target mathematically unreachable, or a value is outside the range the formula is valid for, we say so rather than returning a confident number that would mislead you.
Do you use overseas formulas?
Only where the formula is genuinely international, such as clinical equations for metabolic rate. Anything rate-based, regulated or unit-dependent uses Australian figures and standards, and the page names the source.