Do I need to Use a Calculator during the PMP Exam?

Probably, yes. The exam is not a test of your math skills and if you can do primary school level calculations in your head, you don't need a calculator. However, people are known to stumble on '2+2=4' type calculations also under intense pressure, and it won't hurt to verify your results with a calculator.

Nowadays, the PMP Exam software has a calculator application built into it (as per PMP Handbook). However, I wasn't aware of this when I took the exam and cannot say how well it works. I was given one of those dollar-store calculators with huge buttons and bold display. I wasn't even sure whether it was spitting out correct results. Fortunately, I passed the exam.

Normally, the test centers provide calculators and you are not allowed to carry your own calculator inside the test area. But you might also want to carry your own calculator to the test center, just in case. Most likely, you'll be asked to leave yours outside (in the locker).