Percentage Calculator Tips and Tricks for Everyday Math
Percentages show up in discounts, tips, taxes, and growth. A few mental shortcuts make the common cases fast and reliable. Percentages are everywhere: discounts at the store, tips at a restaurant, tax on a receipt, growth on a report. Most of the time people reach for a calculator, but a handful of shortcuts cover the common cases faster than typing, and understanding them means you can sanity-check calculator output instead of trusting it blind. I have blown enough calculations over the years, usually by rushing, that I now treat percentages as something worth doing slowly and correctly the first time. The Three Percentage Operations You Need Almost every percentage problem reduces to one of three operations. Finding a percentage of a number, like 15 percent of 80. Finding what percentage one number is of another, like 30 out of 80 as a percentage. And finding percent change, like going from 80 to 100. Knowing which operation the problem asks for is half the battle, because the wording is often vague. For the first, multiply by the decimal form of the percentage: 15 percent of 80 is 0.15 times 80, which is 12. For the second, divide the part by the whole and multiply by 100: 30 divided by 80 is 0.375, times 100, which is 37.5 percent.