Percentages and general maths
Percentage handles the three questions that cover almost every real use: what is X% of Y, X is what percent of Y, and the percentage change between two numbers — plus the money cases, mental shortcuts, and the percentage-points distinction that trips people up. Fraction adds, subtracts, multiplies and divides fractions and shows the working, not just the answer.
Dates and time
Age, Date Difference and Days Until cover the three directions you can ask a date question. Time Duration handles the awkward case of hours between two clock times, including shifts that cross midnight, and Work Hours builds that into a weekly timesheet with breaks, overnight shifts and optional pay.
Converters
Converting units is where a calculator beats mental maths, because the conversion factors are rarely round. The Height, Weight, Length, Speed, Temperature and Data Storage converters each show the formula alongside the result, and include a reference table of common values so you can sanity-check the answer at a glance.
Money and shopping
Tip splits a bill including the awkward per-person rounding, Discount handles stacked discounts (two 20% reductions are 36% off, not 40%), and Sales Tax / VAT works in both directions — adding tax to a net price, or stripping it back out of a gross total, which is the one people most often get wrong by subtracting instead of dividing.
Home and vehicle
Paint, Tile & Flooring and Concrete turn room dimensions into the quantity you actually need to buy, including waste allowance and coverage per unit — the numbers that stop you making a second trip. Fuel Cost and Electricity Bill cover running costs, with the electricity tool breaking a bill down per appliance so you can see which one is responsible.
How do I calculate a percentage of a number?
Multiply the number by the percentage divided by 100 — for 20% of 150, that's 150 × 0.2 = 30. The Percentage Calculator does this as you type, and also handles percentage change and "X is what percent of Y".
How do I work out hours between two times?
Use Time Duration for a single pair of times — it handles shifts that cross midnight — or Work Hours to build a full weekly timesheet with breaks and optional pay.
Are stacked discounts the same as adding them together?
No. Two 20% discounts applied one after the other give 36% off, not 40%, because the second applies to the already-reduced price. The Discount Calculator works this out correctly.
Do these calculators work offline?
Yes. The site is a progressive web app, so once you've visited a page it's cached and will work without a connection. All maths runs in your browser.