No, you cannot use a calculator on the Census Test. You are, however, provided with additional paper so that you can do the calculations by hand. Remember, that for the most part the level of the math needed to solve the problems that are included on the Census Test is very simple, perhaps even around 4th or 5th grade math. In many instances you may not even need to do any calculations at all, as just by looking at the math problems you should be able to see which answer is the best or most likely one.
If you do the Practice test you will get an idea of the type of math problems included on the Census test. If you find that there are some that you are not able to do, for example, perhaps you have forgotten how to calculate percentages; you will have time to brush up on them before you take the actual test. This article should help you with a refresher on how to do percentages. Good luck!