Everyday and Shopping Calculators

This plot holds the small sums that come up in ordinary life and never seem worth opening a spreadsheet for. There are three clusters. Money at the till covers tips, percentages, discounts, VAT, sales tax and unit price. Running costs covers fuel, MPG, electricity and subscriptions, which are the recurring numbers people underestimate. Dates and time covers your exact age, the gap between two dates, a countdown, the duration between two clock times and a weekly hours total.

The shopping tools are built around comparison rather than a single answer. Unit price exists because a bigger pack is not reliably cheaper and the shelf label is not always comparing like with like. The discount calculator adds sales tax on top of the reduction, so the number you see is the number at the till. The pizza size calculator is the same idea applied to area, which is where most people's intuition fails, because a 16 inch pizza is not a third bigger than a 12 inch, it is close to twice the food.

Nothing in this category needs an account or a sign-up, every page lands with a worked default already filled in, and the result updates as you type rather than waiting for a submit button. The date tools handle leap years and month lengths properly, so counting from 31 January behaves the way a calendar does rather than the way naive arithmetic does.