The small calculations that come up in shops, restaurants, classrooms and car journeys — done instantly, with the arithmetic shown so you can follow it or check it by hand.
The percentage calculator handles the four questions people actually ask: what is X% of Y, what percent X is of Y, the change between two values, and a discount or markup. The average calculator goes further than the mean, giving median, mode, range and both population and sample standard deviation, with a note on when the median tells the truer story. The tip calculator splits a bill between any number of people, the GPA calculator weights each course by credit hours on the standard 4.0 scale, and the fuel cost calculator works in either MPG or litres per 100 km.