Percentage Calculator is one of those utility apps that you don't realize you need until you need it. The app is not your typical calculator with a numeric keypad and operators. Instead, it's a forumla tool that lets you calculate interest, percentages, loan payments and more.
The app has a straight-forward and efficient UI that makes it easy to navigate the app. Just tap the calculation you want to perform, enter the values and the app does all the calculation for you. You can enter in the equation values or the result and the app will fill in the missing blanks.
The app has a variety of business and everyday calculations, including
simple percentage calculator (5 percent of 40 is 2)
percentage increase/decrease (5 percent decrease from 40 is 38)
convert fractions to percentages (5 / 20 is the same as 25 percent)
My favorite is the price/quantity calculator that allows you to compare the unit prices of two different items, such as a 10 ounce bottle of marinade that costs $5.75 with a 25 ounce bottle that costs $12.50.
Percentage Calculator supports 13 languages and a variety of currencies. It's free and works with both the iPhone and iPad.