Method, sources and limits
How these calculators are built and checked
There is no useful way to judge a calculator from the outside. It returns a number, the number looks plausible, and whether it is right depends on a formula and a set of rates you cannot see. This page is the part you can check.
Everything runs on your device
No calculator on this site sends anything to a server. The arithmetic happens in your browser, the figures you type never leave the machine you typed them on, and there is nothing at the other end to store them because there is no other end.
That is a privacy decision first — salaries, land values and clinical figures get typed into these pages — but it is also why the answers change as you type rather than after a round trip.
It is also the constraint that shapes everything else here. A page that cannot call out to anything has to carry its rates as constants, which means somebody has to keep checking them. That is the trade this whole site is built around.
Where the numbers come from
Calculators here fall into two groups, and the difference matters more than it sounds.
The first group is fixed formulas. The volume of a cylinder, the conversion between kilojoules and calories, a compound growth projection — these do not change and cannot go stale. The formula is printed on the page and you can check it against any reference you like.
The second group depends on a figure somebody publishes: a tax threshold, a levy rate, a consumer price index, a gazetted holiday date. Every one of those tools names the authority that publishes the figure, links to the page it appears on, and shows the date we last read that page.
- Australian Taxation Office — income tax rates, luxury car tax thresholds, redundancy and ETP caps, FBT
- Revenue NSW and the State Revenue Office of Victoria — land tax thresholds and rate schedules
- Fair Work Ombudsman and the National Employment Standards — leave accrual
- Transport for NSW and the WA Department of Transport — registration fee schedules
- Department of Home Affairs — skilled migration points test
- Inland Revenue — New Zealand income tax brackets, ACC earners' levy, KiwiSaver settings
- Stats NZ — Consumers Price Index
- NZ Transport Agency and Employment New Zealand — driving limits, holidays and entitlements
- Standards Australia and the National Construction Code — ramp gradients, stair geometry
- MBIE and NZ Building Code guidance — decking spans and joist spacing
How often rates get re-checked
Different figures move on different clocks, so a single review schedule would either be wasteful or too slow. Instead each tool is checked against the cycle that governs it.
| Figure | Set by | Checked |
|---|---|---|
| Australian income tax, LCT, redundancy caps | ATO | Each July, at the start of the financial year |
| Land tax thresholds | Revenue NSW / SRO Victoria | Each July, and on any announced change |
| Fringe benefits tax figures | ATO | Each April, at the start of the FBT year |
| NZ income tax and ACC levy | Inland Revenue | On any announced bracket or levy change |
| NZ Consumers Price Index | Stats NZ | Quarterly, on release |
| NZ public holidays | Gazetted | Yearly, adding the following year |
| Skilled migration points | Home Affairs | On policy change — monitored, not scheduled |
The date on each page is the date somebody actually opened the source and read it, not the date the site was last rebuilt. If a rate has moved and we have not caught it yet, that date is how you find out before you rely on the number.
You can override any published rate
Every rate-dependent tool has an editable rate panel. It exists for two situations a fixed calculator handles badly: working out an earlier financial year, and working with a change that has been announced but has not started yet.
When you change a rate, the tool says so — the result is flagged as no longer based on our verified figures until you reset it. That flag is deliberate. A calculator that quietly uses whatever was last typed into it is worse than one that will not let you type at all.
What is deliberately not here
Some things people search for cannot be built accurately as a static tool, and building a plausible-looking version anyway is worse than leaving the gap.
- Three Australian electrical calculators — maximum demand, cable current carrying capacity and voltage drop. The tables live in paywalled AS/NZS standards and the consequences of a wrong answer are a safety matter for a licensed electrician.
- Credit card limit estimators. Bank serviceability models are proprietary and unpublished, so any figure would be a guess dressed as a calculation.
- Caravan tyre pressure. Real accuracy needs manufacturer load and pressure tables per tyre model, and a generic formula on a towing safety question is not a reasonable thing to publish.
- Insurance premium quotes. No public pricing data exists to compute one from.
Errors, and how to report one
Numbers here will be wrong sometimes. A threshold moves and we are slow, a formula edge case turns out to behave differently, a source page changes its wording. The useful thing is how fast that gets fixed.
The most valuable report names the calculator, the figures you put in, the answer you got and the answer you expected. A link to the authority that publishes the correct figure turns a report into a fix on the same day, because it removes the part that takes longest.
Corrections go to the same place as everything else — get in touch, where a person reads what you send. No form, no account, no ticket number.