I was recently looking for a simple percentage calculator for iPhone and I came across OffOf, an app developed by Daeo Corp. and available for free on the App Store.

As the name suggests, OffOf lets you calculate the percentage off an amount or the percentage of an amount. While this operation is possible with any calculator, OffOf has a visual interface with buttons to switch calculation types with a single tap. If you want to calculate how much a $50 t-shirt is going to cost you at “25% off”, select the Off button, tap percentage and enter a number, then tap Amount and the app will calculate it in real time. On the other hand, if you have to know how much the 20% of 135 corresponds to, you can choose the Of type and let the app calculate it for you with no additional manual operations.

My main concern with OffOf is that, in an effort to provide a colorful iOS 7 design (reminiscent of Numerical), it’s hard to distinguish the selection state for the Percentage and Amount fields. The app uses a white highlight for numbers in those areas, but I find it hard to parse when compared to the light gray used for the non-selected state. It’s a minor problem, but it confused me when I started using the app.

OffOf won’t become a hit among calculator power users, but, for me, is solves a common problem, and it’s free on the App Store.