Who this is for
Subscription businesses carry two different margin stories. Serving an existing subscriber is usually cheap: hosting, support, and success costs against their monthly fee produce software-style gross margins. Acquiring the next subscriber is expensive, and the net margin after sales and marketing tells you whether growth is being bought at sustainable prices.
Enter MRR as revenue, the costs of serving subscribers as cost of goods sold, and everything else, including acquisition spend, as operating expenses. The two margins the calculator returns map exactly onto the two stories, and the churn notes below explain why the same numbers can be healthy or alarming depending on retention.