Calculator Tools

Accurate by design

Everyday money maths, made clear.

Calculator Tools is a collection of free online calculators. We turn standard financial formulas into simple tools that help you work out tips, savings, loans, and mortgages with confidence.

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01Who we are

Tools for the numbers behind everyday decisions

Calculator Tools brings together standard formulas,plain-language explanations, andsimple, accessible design to help you make money decisions with confidence.

02What you get

Built on three things that matter

Whatever the calculator, these are the standards it is measured against.

  1. Accuracy

    Standard financial formulas, checked against worked examples before a calculator goes live.

  2. Clarity

    Results, assumptions, and formulas are shown in plain language, so you can see how each number is reached.

  3. Privacy

    Calculations run in your browser. The figures you enter are not sent to a server.

03What we believe in

Four principles behind every calculator

These values guide what we build and how we explain it.

  • Accuracy first

    A calculator that is wrong is worse than none. We test every formula against known results.

  • Plain language

    Labels, hints, and error messages are written for people, not accountants.

  • Show the working

    Each calculator explains its formula and assumptions, so you can judge the result for yourself.

  • Made for real decisions

    From splitting a bill to paying off a mortgage, we focus on the numbers people actually need.

04How we work

From question to finished calculator

Every calculator follows the same four stages, so you can trust what you get.

  1. Research

    We start with the question people are trying to answer and the standard formula behind it.

  2. Build

    We turn the formula into a fast, accessible calculator that works on any device.

  3. Test

    Results are checked against worked examples, and empty or extreme inputs get clear messages.

  4. Explain

    Each calculator comes with a guide that covers the formula, assumptions, and common questions.

05Our calculators

Pick the one that fits your question

Each calculator has its own page with a guide, so you can see how the numbers are worked out.

Have a question or a calculator in mind?

Tell us which calculator you would like to see next, or let us know if something looks wrong.

Get in touch

Our calculators give estimates for learning and planning. They are not financial, tax, or legal advice.