Anjum,
There is a calculator built into the test software. When I took the exam they also gave me a calculator. However, I strongly recommend that you contact the test center that you will be using to confirm what they will provide. It's also a very good idea to visit there personally ahead of time if at all possible. I did so, and found that it greatly reduced my anxiety on test day - knowing where to drive, where to park, and precisely what to expect inside. Prometric offers a "Test Drive" in my area that I took advantage of. For $30 they take you thru the process, give you a test exam (non-PMP related) so you can see how the test software works, and they even walk you thru the check-in procedure. It was $30 well spent, in my opinion.
Good luck!
Tracy