I feel students should be using calculators as little as possible. In my experience this improves number sense.

When I teach a class, below Algebra, I do not allow calculators (except for finding the square root of non-square numbers.) If a student did not have their multiplication mastered after 3rd grade, I will let them use a multiplication table for tests.

In algebra I do not use graphing calculators. Too many students do not fully understand what is happening in a graph, such as the need for even spacing. I like to have calculators that do not use order of operations for them.

When a student reaches Advanced Algebra (Algebra 2) there should be calculator days and non-calculator days.