Yes calculator is allowed in exam but it would be computer calculator like you have in your computer in Windows. The calculator button is present on top of the test portal, when you click that you will see a calculator and you can use the same way that Windows has.

In Prometic exam centre, you will not be allowed to even carry your handkerchief. Except the locker key (where you can keep all your belongings), your photo ID proof, and the dress you have wore, nothing else you can carry in the exam room, not even drinking water.

Saket, PMP