The phrase "per calendar month" is commonly used to indicate the frequency of expenses, salary, and other payments. But, at times, it becomes monotonous to use the same phrase repeatedly. Luckily, there are several synonyms for "per calendar month" that can add some variety to your language. You may choose to use phrases such as "monthly basis," "every month," or "monthly installment" instead. Additionally, you can use other synonyms such as "per month," "monthly rate," "monthly subscription," and "monthly charge." Using these synonyms not only adds variety to your writing but also makes it easier to understand for readers who prefer simpler language.