Everyday Calculators
Fast, no-nonsense calculators for the arithmetic that comes up in real life. Working out a percentage change, checking exactly how old someone is, counting the days until a deadline, or splitting a restaurant bill without the awkward pause. Every calculator shows its working so you can sanity-check the answer.
Most everyday arithmetic is not hard, it is just fiddly enough that doing it in your head produces a number you do not quite trust. Percentages invert in ways that surprise people, months have different lengths, and working days are not calendar days. These tools handle the fiddly part and, more usefully, show the working so you can see why the answer is what it is.
Start with the percentage calculator if you are checking a discount, a tip, a tax line or a change between two figures. It covers all four directions, including the one people get wrong most often: a 20 percent fall followed by a 20 percent rise does not return you to where you started. The fraction calculator does the same job for anything expressed in halves and thirds, which is most recipes and most woodwork.
For anything involving dates, the distinction that matters is between calendar days and working days. A deadline six weeks away is forty two calendar days and about thirty working days, and that gap is where a great many missed deadlines live. The countdown and date difference tools show both. The age calculator handles the leap-year edge cases that catch out manual counting, and the time duration calculator adds up hours and minutes without the base-60 mistakes.
The DIY calculators here work from measurements to materials: concrete volumes, stair rise and going, paint, wallpaper and flooring quantities. Each one includes a waste allowance, because ordering the exact calculated amount is how a job stops halfway through. Where a calculation is governed by building regulations, the tool names the rule it is checking against and the jurisdiction it applies to.
Everything runs in your browser. Nothing you type is uploaded, there is no account, and every tool states its formula in the page so you can reproduce the result by hand if you want to check it.