# Can you build a calculator that helps customers understand a decision? Canonical URL: https://newphysician.org/can-you-do-this/build-a-custom-calculator/ Yes, when the calculation can be explained and its assumptions are visible. A useful calculator helps someone explore a decision; it should not present a rough model as a personalized professional recommendation or a guaranteed financial result. What a solution might involve Agree the inputs, formula, units, rounding, and treatment of missing values. Show assumptions and sensitivity where they matter. Test known examples and boundary conditions, then make the interface usable on a phone with clear labels and understandable results. What needs care Precise-looking numbers can create false confidence. Default values, exclusions, and time horizons should be visible. If the formula is disputed or requires regulated advice, clarify that boundary before building an attractive interface around an unsupported model. How we would judge whether it works Approved examples produce expected results, invalid inputs are explained, and changing an important assumption changes the output predictably. The result identifies its limitations and does not require visitors to disclose unnecessary personal information. Likely engagement Rapid Build: $1,500 to $3,000. This is a likely starting tier, not a quote. Scope, access, dependencies, and responsibility for operation need agreement first. Discuss Rapid BuildWhat to send first Bring the decision, formula or worked examples, intended audience, and assumptions that users commonly misunderstand. Send me the messy version. Experience and scope Selected builds documents the currently authorized public proof. This page describes a proposed approach, not a claim of a completed client engagement in this exact workflow. Related problems Can you turn a small idea into a working digital product? Can you build a dashboard that helps us decide what to do next? [Send me the problem](https://newphysician.org/send-me-the-problem/)