Estimates, not advice
Every number on this site is an estimate produced by applying published rules or standard arithmetic to the values you entered. It is meant for understanding a rule and comparing two options. It is not tax advice, legal advice or financial advice, it is not a quotation from any lender, and it is not a statement of what any tax authority will charge you.
The difference matters in one direction in particular. A calculator can tell you what a rule does to a salary. It cannot tell you what you should do, because it does not know your circumstances and never asks: your other income, your reliefs, your dependants, your history, your obligations, what you already owe and what you already own. Advice starts where those questions begin.
Statutory calculators: sourced, dated, and still not your tax return
Where a page applies rules somebody published — income tax bands, social insurance ceilings, withholding tables, student loan thresholds — every figure traces to an official document, and the page names the document, the tax year it applies to and the date the data file was last checked against it. Read those three things before trusting a result. They are on the page because they are the difference between a number you can check and a number you have to believe.
Even a correctly implemented rule gives a figure that is not your payslip. The calculators assume the standard case for a jurisdiction unless you change the options shown. Real payroll is shaped by things the page is never told: a mid-year start or leave, a code carried over from a previous employer, benefits in kind, a pension scheme, a second job, a mid-year change in the law. Where your payslip and this site disagree, the payslip describes your actual position. Where a tax office assessment and this site disagree, the assessment is the one that is enforceable.
A tax year updates once a year and rules occasionally change inside one. Between the day a rule changes and the day the data file is updated, a page can be out of date while still showing the date it was last checked. That date is the honest signal, and it is shown for exactly this reason.
Formula calculators: a stated convention, not a lender's quote
Where a page applies arithmetic that is nobody's rule — a loan payment, compound growth, a rate of return, a margin, a deposit — there is no authority behind it and none is claimed. The page states the formula, the convention it chose where more than one is defensible, and the things it does not account for. Those statements are the whole basis for the number.
Two consequences are worth spelling out. A rate a page computes from what you typed is not an APR or an APRC: those are legally defined figures that fold in fees and charges the page never asked about, and a lender must quote them to you itself. And a projection is not a forecast. A growth calculator shows what a rate would produce if it held for the whole period, which no real return does; it is a way of seeing the shape of compounding, not a prediction about markets.
Commercial rates go out of date
Where a page shows a market average or a product's published terms, it says when that figure was collected, and it stops showing it once it is too old to stand behind rather than quietly ageing on the page. Any such figure is a starting point for a form field, never an offer. What you will actually be charged depends on your credit, the product and the lender, and only the lender can tell you.
What to do with a number from here
Use it to compare options, to sanity-check an offer, to understand what a threshold does, or to see whether a plan is roughly viable. For a decision that turns on the exact amount — signing a contract, accepting an offer in another country, filing a return, borrowing — check it against the authority that will collect it, the lender that will charge it, or an adviser who can be told everything. That is not a formality: crossing a border adds residency rules, treaties and social insurance arrangements that no calculator on this site models.
If a figure looks wrong
Report it. The contact page says what to include, and the most useful thing is the official document your expected figure comes from, because that is what a statutory page can be checked against. An error on a page affects everyone reading it, so a report that can be verified is acted on ahead of almost anything else.