Open calculator library
Open formulas behind practical UK business calculators
PoundKit publishes transparent formulas and test cases behind its calculators so users and developers can understand how calculations work.
Open-source calculator library
PoundKit publishes the formulas, calculation logic and test cases behind its free UK business calculators. Users and developers can review the implementation on GitHub.
Calculator library
VAT Calculator
UK VAT calculation formulas including adding VAT, removing VAT and VAT breakdown examples.
Open calculator →Profit Margin Calculator
Transparent profit margin formulas with example calculations.
Open calculator →Break-even Calculator
Break-even point calculation logic and test examples.
Open calculator →Freelance Rate Calculator
Freelance pricing calculation methodology and examples.
Open calculator →Self Assessment Tax Calculator
Income Tax and Class 4 National Insurance estimation logic with automated test cases.
Open calculator →For developers
PoundKit calculator logic is designed to be transparent and reusable. We publish formulas, test cases and implementation examples for developers building business tools.
Repository URL: https://github.com/Poundkit01/uk-business-calculators
Why we publish our formulas
Users can verify how calculations work
Developers can reuse tested logic
Business tools become easier to trust
These formulas are published for transparency and education. They are not HMRC approved, accountant verified or official government formulas. Always check GOV.UK or speak to a qualified professional for your specific situation.
More transparency resources
Calculator Formula Library →
Every formula behind the PoundKit calculators, with worked examples.
Formula Test Cases →
The inputs and expected outputs we use to verify calculations.
All Calculator Tools →
Try the VAT, margin, break-even and freelance rate calculators.
PoundKit Data Library →
Original datasets and benchmarks for UK freelancers and small businesses.