Free Online Calculators

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Guides for common jobs

• Build a gaming PC — Six calculators that check a gaming PC build from PSU to aim.
• Buying a house — Eight calculators that walk through the money side of buying a home.
• Garden landscaping project — Ten calculators that size the materials for a garden landscaping job.

How the calculators are organised

Everyday Maths covers the arithmetic people reach for most often: percentages, discounts, unit conversion, margin and markup, and a full scientific calculator for everything else. These are the tools you want when a figure needs checking in the middle of something else.

Loans & Savings is where money over time lives. Loan and mortgage repayments, compound interest, currency conversion and salary conversion all share a trap: the same number means different things depending on the convention behind it. Each page states its convention before it gives you a figure.

Dates & Time handles calendar arithmetic — age, the gap between two dates, working days and time zones. Months and years are not equal, so these tools count directly rather than approximating from an average month.

Health holds BMI and daily energy expenditure. Both are population-level estimates, useful as a starting point and for comparing one period against another, and each page says where the formula stops being reliable.

Home & DIY turns a measured area or volume into a quantity you can order — concrete and paint, with the waste allowance that saves a second trip. Imperial measurements can be typed the way you say them, so 5'10" is understood as-is.

Why the maths runs in your browser

Every calculation on this site happens on your device. Nothing you type is sent anywhere, which matters most for the financial and health tools — your salary, your loan balance and your weight never leave the machine you are sitting at. It also means the tools work with a poor connection, or none at all once the page has loaded, and results appear as you type instead of after a round trip to a server.

Precision and rounding

Results are rounded for display, not during the calculation, so intermediate steps keep their full precision and the final figure does not drift. Where a result depends on an assumption — a compounding frequency, a working week, a coverage rate per litre — the assumption is written on the page rather than buried in the code, so you can check whether it matches your situation before you rely on the answer.

What to do if the calculator you need is missing

The subcategory pages each list every tool in their group. If none of them fits, the scientific calculator handles arbitrary expressions, and the business section has a further set of pricing, profit, invoicing and tax calculators aimed at freelancers and small companies.

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