Methodology

Where the formulas come from

Every calculator implements a standard, published formula for its subject — the same amortisation, compound-interest, unit-conversion or statistical expressions found in textbooks and public references. We do not invent proprietary models, and we do not weight results toward any product or provider.

806 of our 817 calculators publish the formula they use directly on the page, in a Formula & Mathematical Calculation section, so you can check the arithmetic yourself rather than trusting the output.

What runs where

Calculations run in your browser in JavaScript. When you press Calculate, no HTTP request carries your inputs anywhere: the numbers you type are not transmitted to our servers, not written to a database, and not shared with a third party. You can verify this in your browser's network panel — press Calculate with the panel open and no request appears.

The practical consequences: nothing is saved between visits, results cannot be recovered if you close the tab, and no account is needed or offered. Every calculator is free, with no usage limit and no paid tier.

What the results assume

A calculator can only work with what you give it. Each tool page carries its own Assumptions & Limitations section, and these apply throughout:

• Every value you enter is treated as exact and already known.
• A rate or interval is assumed to hold for the whole period unless the form asks for it separately.
• Only the values on the form affect the result. Fees, penalties, promotional terms, tolerances and local adjustments that have no input field are not modelled.
• Figures are rounded for display; the underlying arithmetic uses your full precision.
• Results are returned in the units or currency you enter — the tools are unit-agnostic unless a page states otherwise.

What we do not do

Being clear about this matters more than sounding authoritative:

• No financial, legal or tax advice. A result is an estimate for planning and education, never a quote, an offer, or a recommendation. For decisions that carry lasting consequences, confirm the numbers with a qualified professional.
• No live rates or market data. Nothing on this site fetches current interest rates, prices or tax tables. Any rate used in a calculation is one you typed in.
• No personalised recommendations. We do not profile you, score you, or rank products for you.
• No jurisdiction guarantee. Tax rules, lending regulations, measurement standards and conventions differ by country and change over time. Check the rules that apply to your own situation.

How the library is organised

There are 817 calculators live across 23 categories, from mortgages and taxes to unit conversion, health, statistics and date arithmetic. Depth varies by page: some carry a worked example and tool-specific questions, others currently show the formula and the calculator alone. We are filling that gap category by category rather than padding pages with generic text, so a page that is thin today says less rather than saying more of nothing. Browse everything from the calculator catalog.