Your nook for
smart tools

Who builds ToolsNook, and where the numbers come from

ToolsNook is built, written and maintained by one person — not a content farm, and not an anonymous brand. Every calculator here exists because it was needed first, in a real business, before it was ever a web page.

Formulas come from primary sources

Where a number has an issuing authority, we take it from that authority and link to it so you can check. VAT rates come from HMRC. BMI thresholds come from the NHS and the NIH. Password guidance comes from NIST and the NCSC. Statutory late-payment interest comes from the Late Payment of Commercial Debts Act. Unit conversions come from the SI Brochure. Nothing here is sourced from another blog quoting a source.

Every page states the formula it uses in plain text, so you can check the arithmetic on paper. Each implementation is tested against worked examples before it goes live, and the two errors that catch people most often — confusing markup with margin, and inclusive with exclusive date counting — are tested for specifically.

We use AI, and we say so

The written explanations beneath each calculator are drafted with AI assistance, then edited, fact-checked and published by a named human. The five AI writing tools generate their output on demand and it is nobody's finished draft but yours. AI does not choose our formulas, set our rates, or publish anything unread. The full process is documented on the methodology page.

Guides

Some questions need more than a calculator. Our guides work through the reasoning behind the numbers:

• Markup vs margin — why a 50% markup is only a 33.3% margin, and what that confusion costs a real business.
• How to set your freelance rate — the formula that accounts for tax, expenses and the hours you can't bill.
• Break-even analysis — exactly how many units you must sell before you make a penny.
• VAT for small businesses — the £90,000 threshold, the rolling test, and when you must register.

Free, and honest about why

There are no accounts, no paywalls and no subscriptions. The site is funded by clearly-labelled display advertising. No advertiser has ever paid for a mention, a placement or a recommendation, and if that ever changes it will be disclosed before it happens. Your calculations never leave your browser — there is no server behind these tools to send them to.

Last reviewed: 9 July 2026 · Corrections: hello@toolsnook.com