Sources & references

Where the numbers, formulas, and thresholds on Calclens come from. We use authoritative UK and international sources only — no scraped data, no other calculator sites.

The references below are grouped by the category of calculator they support. Each individual calculator page also links to the specific source it uses, but this is the master list. If you spot a missing or outdated reference, please let us know.

Finance

Mortgages, loans, savings, tax, salary, VAT, stamp duty, investment.

  • HM Revenue & Customs (HMRC) — gov.uk/hmrc. Income tax bands, National Insurance contributions, PAYE thresholds, VAT rates, capital gains, dividend tax.
  • Financial Conduct Authority (FCA) — fca.org.uk. Mortgage market guidance, consumer credit rules, regulated firm definitions.
  • Bank of England — bankofengland.co.uk. Base rate, historical rate data, inflation series used for real-return calculations.
  • Money and Pensions Service (MoneyHelper) — moneyhelper.org.uk. Reference figures for typical UK household finances, pension allowances, savings benchmarks.
  • HM Land Registry — gov.uk/land-registry. Stamp Duty Land Tax thresholds, property price statistics.
  • Office for National Statistics (ONS) — ons.gov.uk. Average earnings, household income, CPI/CPIH inflation, regional cost-of-living data.

Health

BMI, body fat, calorie needs, hydration, pregnancy dating.

  • National Health Service (NHS) — nhs.uk. BMI thresholds, healthy weight ranges, daily calorie recommendations, hydration guidance, pregnancy due-date methodology.
  • National Institute for Health and Care Excellence (NICE) — nice.org.uk. Clinical guidelines for adult obesity classification, ethnic-specific BMI thresholds.
  • World Health Organization (WHO) — who.int. International BMI classification, growth standards, hydration baselines.
  • Mifflin-St Jeor equation — Mifflin MD et al. (1990), American Journal of Clinical Nutrition. Basal metabolic rate formula used in our BMR and TDEE calculators.
  • British Dietetic Association (BDA) — bda.uk.com. Macronutrient distribution ranges and fluid intake guidelines.

Maths & science

Percentage, fractions, statistics, geometry, scientific calculation.

  • Khan Academy — khanacademy.org. Cross-checking standard formulas and worked examples for clarity of presentation.
  • NIST Digital Library of Mathematical Functions — dlmf.nist.gov. Reference implementations of trigonometric, logarithmic, and statistical functions.
  • Standard textbooks: Stroud, Engineering Mathematics; Spiegel, Schaum’s Statistics; OpenStax College Algebra. Used for formula derivations.

Business

Profit margin, break-even, VAT, salary take-home, freelancer day rate.

  • Companies House — gov.uk/companies-house. Reference for company filing thresholds and accounting period rules.
  • HMRC business tax guidance — gov.uk/business-tax. Corporation Tax rates, VAT registration threshold, IR35 reference.
  • Institute of Chartered Accountants in England and Wales (ICAEW) — icaew.com. Standard definitions for gross margin, contribution margin, break-even analysis.
  • Office for National Statistics (ONS) — labour market and earnings statistics used as benchmarks for day-rate calculators.

Everyday & conversion

Tip, age, date difference, fuel cost, currency, time zones.

  • UK Department for Transport — gov.uk/dft. MPG conversion methodology, fuel duty rates.
  • IANA Time Zone Database — iana.org/time-zones. Authoritative time-zone data used in date and time conversions.
  • BIPM (Bureau international des poids et mesures) — bipm.org. SI unit definitions used for unit conversions.
  • European Central Bank — ecb.europa.eu. Reference exchange rates (where live data is not used).

Construction

Area, materials, paint coverage, concrete volume.

  • British Standards Institution (BSI) — bsigroup.com. Building standards, materials specifications.
  • RICS (Royal Institution of Chartered Surveyors) — rics.org. Measurement standards for area and volume in UK property.
  • Manufacturer data sheets — for paint coverage, concrete mix ratios, and similar product-specific values, we use published manufacturer specifications and note this on the relevant calculator page.

Disclosure

Linking to a source is not an endorsement, and being listed here does not mean a source endorses Calclens. We do not receive payment, sponsorship, or any other commercial benefit from any organisation listed above. None of these references is an affiliate partner.

If a calculator on Calclens relies on a source that’s not listed here, that’s an oversight we’d like to correct — please let us know so we can update this page.

Curious about how we build the calculators?

Our methodology page walks through the six-step process every calculator goes through before going live.

Last updated: May 2026

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