I never had a hard and fast rule about no calculators. I allowed them when my kids did the Singapore Challenging Word Problems books. They loved it because they felt like they were getting away with something. I also allowed them once they got to Algebra I. I had the older one do some arithmetic review after starting Algebra I, and he wasn't allowed a calculator for that. I'll probably do the same for the younger one. They both started Algebra I and age 10-11.