How BriskCal calculates
Every figure on this site is arithmetic over published rules. This page explains where the rules come from, how you can tell whether they are current, and what happens when they are not.
Every rate comes from a published source
British income tax, National Insurance and student loan repayments are not estimates or models. They are bands, thresholds and percentages published by HMRC and the devolved revenue bodies, and either a calculator uses the right ones or it does not. There is no interpretation involved and therefore no excuse for getting it wrong.
So no figure is typed into this site from memory. Each tax year is transcribed from the government page that publishes it, that page is linked from every calculator that depends on it, and the link goes to the source rather than to a summary of the source. The reference shelf is at the bottom of this page.
Every page is dated, and the date means something
A calculator running last April's thresholds looks exactly like one running this April's. That is the whole problem with this category: the failure is invisible from the outside, so the only defence is for the page to state when a human last looked, and for that statement to be true.
Each calculator says which tax year it uses and the day the figures were last checked against the sources. "Last checked" is not the publication date and is not generated at build time. If nobody has checked a page since the tax year it claims to describe began, it is not a page that has gone slightly stale — it is a page describing a year it has never seen.
A page that has not been checked stops asking to be found
That rule is enforced by the build rather than by anybody's diligence. A calculator page has to carry a
stated tax year, at least two cited sources, its own written explanation and a check date on or after the
start of the year it describes. Miss any of those and the page still works — the calculator is the same
calculator — but it carries noindex and disappears from the sitemap until the gap is filled.
This costs traffic, on purpose. Rates change every April, maintenance is a commitment rather than a task, and the alternative to a page quietly leaving the index is a page quietly publishing figures that stopped being true.
Nothing you type is sent anywhere
Your salary is nobody else's business. Every calculation runs in your own browser; there is no server to send it to, no account, and nothing stored. You can confirm that rather than believe it — open your browser's developer tools, watch the Network tab, and use a calculator. Nothing goes out.
What this site will not do
It will not tell you what to do with the answer. Working out that you would keep a certain amount is arithmetic; saying you should therefore remortgage, or salary-sacrifice, or change pension provider is regulated financial advice, and a calculator is not the thing that gives it. Where a figure depends on a choice, the page explains what the choice changes and leaves it with you.
Questions about the method
Who writes this?
BriskCal is published by BriskLabz. There is no named author, and that is a deliberate choice with a real cost attached: Google's guidance on money content rewards an identifiable person with a stated reason to be trusted, and a brand is a weaker signal than a person.
The argument for it is that this site's case rests on things you can check rather than on credentials you would have to take on faith. Every rate links to the government page it came from. Every page carries the date a person last checked it. The calculation engine is open source, so the arithmetic can be read by anyone who doubts it. A biography would tell you who to trust; this tells you how to verify.
What does "last checked" actually mean?
That on that date a person opened the linked source and confirmed the figures this site uses still match it. It is not the date the page was published, not the date the site was deployed, and never a build timestamp — a page claiming to be revised every night while saying nothing new is a spam signal, not a freshness one.
What happens when the rates change in April?
Each tax year is a separate data file, so bringing a year in is editing data rather than changing code. Until somebody has done that and dated the check, any calculator claiming to describe the new year automatically stops asking to be indexed and drops out of the sitemap. The build enforces it; nobody has to remember.
Why will you not tell me what to do?
Advising on financial matters in the UK is a regulated activity under the Financial Services and Markets Act 2000. Working out arithmetic is not. "Your take-home pay would be X" is a calculation; "you should salary-sacrifice into your pension" is advice, and this site does not say it — not as a nudge, not as a suggested next step, not in a heading.
I think a figure here is wrong.
Then say so, and say which page and which figure. A calculator that is wrong is worse than no calculator, and the failure is silent — nobody reports a bad number, they just leave. Corrections are the most useful thing anyone can send.
The reference shelf
- Income Tax rates and Personal Allowances: Current rates and allowances
- National Insurance rates and categories: Contribution rates
- Repaying your student loan: How much you repay
- Rates and thresholds for employers 2026 to 2027
- Stamp Duty Land Tax: Overview
- Land and Buildings Transaction Tax
- Land Transaction Tax rates and bands
Each URL above was requested on 21 August 2026 and returned the page named. No rates have been transcribed from them yet, so none carries a check date — the first will appear alongside the first calculator.