This is a very popular question, and the answer often elicits an audible sigh of relief. So, yes, you can use a calculator. But the ability to calculate every problem is far from a boon.
First off, many problems do not require a calculator. In fact, using a calculator may very well slow you down, because you can either do the arithmetic faster in your head or on a piece of paper. Then, there is always the case of what to calculate. While a calculator won’t make a careless error (unless you enter in the wrong number), neither will it summon the approach to a very difficult problem. Basically, the GRE math is still testing your ability to logically deconstruct a problem. In many cases, the challenge is not the math, but the approach to a problem.
When is it Advantageous to Use a Calculator?
There are times when the sum is simply too difficult to multiply on paper, and the question is not asking for an approximation. Problems such as compound interest come to mind. Perhaps you have to find the hypotenuse of a right triangle with sides of 51 and 31. Figuring out the square root of a large number could be very difficult without a calculator.
Of course, if the problem asks what is the units digit of 3^1000, then you then have to come up with a clever way to approach the problem—a calculator does not hold that many digits.
For shortcuts and tips on how to use the new GRE calculator to your best advantage, read our post on Calculator Strategies for the Revised GRE
Getting a Feel for the Calculator
The best way to determine whether you will benefit from a calculator is to take a practice test using Magoosh GRE or the new GRE CD (for those with Macs please read here). By doing so, you should get a feel for the number and types of questions in which the calculator will help you save time, and those in which using it will only eat up time.
This frequently asked question and all others are answered in our new GRE Guide!