Since CAT 2015 an onscreen calculator is provided in the exam. A scientific calculator was provided in CAT 2015 and since CAT 2016, the onscreen calculator has some limited operations like addition subtraction, multiplication and division. It also has some functionalities like square root and reciprocal.
The onscreen calculator can also be moved around the screen and it can be closed and opened by clicking on the calculator button in the exam interface. You can see a replica of the calculator available in the exam below. Click on the View Calculator button to practice using the calculator in the exam.
You can also take a free mock to use the calculator in an exam environment to practice betterTake a Free MockCAT