Calcute: Freeware Portable Calculator 11.4.28 - Download Latest Version

Calcute is the best calculator available at the moment. And yes, it's portable.

Portable info:
Use the setup program to extract the executable and help file to the directory you specify. You can copy the calcute.exe program file (and the calcute.chm help file if you wish) to a thumb drive. Then, un-install your desktop version if all you need is a portable calculator.
Or just simply extract with 7zip, winzip, winrar, etc. to any folder and use it as portable application.