Methodology
How each calculator here is built, and why you can check every figure yourself.
The law lives in one place
Every statutory rule the arithmetic uses is written in a rules file kept apart from the code, and each entry carries three things: what the rule says, the article it came from, and the date it took effect. No rate, no period and no ceiling is written inside the code itself.
The effect is practical. An amendment means one line in a rules file and a new date, not a code review. It also means a page cannot state a rule its own calculator does not use, because the formula shown on the page is generated from the same file the calculator reads.
The arithmetic is a function, not a service
Each calculator is a function that takes the rules and your inputs and returns an answer. It reads nothing, writes nothing and calls nothing, which is what makes it testable against worked examples, and that is what we do: every calculator is covered by tests comparing its output with figures worked out by hand from the text of the article.
It all runs in your browser. Your salary, your length of service and the size of your room never leave your device and reach no server. There is no account and nothing to sign in to.
A rule and a price are different things
Some numbers are rules: the end-of-service rate, the notice period, the ceiling on contributory wage. They change by amendment, they have a known effective date, and they are shown as they are with no way to edit them.
Others are prices: a bag of cement, a square metre of building, a gram of gold. Those are not rules but estimates, and they go stale quietly, so they arrive as editable fields with the date they were last checked printed underneath. The price that belongs to your project is the one you were quoted.
What every page shows
Each calculator page shows the formula itself, ready to copy; a worked example step by step; an explanation of what the tool does; questions answered with figures rather than generalities; the articles used; and the date it was last reviewed.
The point is that you can check the number yourself, or copy the formula into a message to an employer. A tool that shows only an answer is asking to be trusted. A tool that shows its working can be checked and argued with.
Review, and what has not been checked yet
Rules are reviewed annually and whenever an amendment is announced; prices are reviewed whenever the market moves noticeably. The date of the last review sits at the bottom of every page rather than somewhere out of sight.
Some entries still need a final check against the official text, and they are marked as such on the sources page. Saying so plainly is better than presenting a confidence nothing has verified.
What these tools do not do
They give no legal, financial or religious advice and replace no professional. The results are estimates built from what you enter and the rules shown, and your actual position may differ with your contract and the facts of your service.
And they do nothing on your behalf: no transfer, no claim, no message to anyone. This is a calculator. The decision and the action stay with you.