An unlimited plan has a fixed revenue per customer and potentially variable usage. Its economics depend on how customers actually behave, especially the minority who consume substantially more than the average. A profitability calculator can expose that risk; it cannot guarantee a future usage distribution.
Model the upper tail
Suppose normal usage costs $1 per month and heavy usage costs $10. With 10% heavy customers, average usage cost is $1.90. With 25% heavy customers it is $3.25. At 50% heavy customers it reaches $5.50. The normal user’s cost stayed constant, but the customer mix changed the business.
If the subscription is $5, the last case loses money on usage alone. Payment fees and infrastructure worsen that result. More customers do not fix a negative contribution per customer under unchanged assumptions.
Free users are part of paid economics
If every paying user supports two free users costing $0.20 each, another $0.40 belongs in the per-paying-customer cost. This subsidy depends on conversion and relative activity. A free plan that is inexpensive at 50% conversion can become expensive at 5% conversion.
Enter monthly active users and the fraction who pay, then explicitly set free usage. Do not divide costs only by paying users while forgetting the free cohort’s consumption.
Margin is not the same as profit
A positive contribution margin means revenue exceeds the entered variable costs. Fixed operating costs still need to be covered. Break-even estimates how many paying customers cover those fixed costs while holding usage and conversion constant. If contribution is nonpositive, the tool reports no finite break-even.
Make the product promise concrete
Use measured billing to test the cost of the promise you intend to make. Included credits, clearly described fair-use rules, and paid usage beyond an allowance can each produce different economics. The calculator does not implement or recommend deceptive limits; it helps you compare the numbers before you choose and disclose a plan.
Save a baseline, a higher-heavy-user case, and a lower-conversion case. Compare their contribution and profit, then decide whether your proposed price leaves enough room for uncertainty.