Describe the formula with examples
For each parameter, set units, minimum, maximum, and allowed combinations. Separately describe the minimum payment, shipping, installation, discounts and taxes if applicable. Prepare control examples: simple, extreme and non-standard. The formula in the table should match the business rules and not be a rough sketch.
Continue with: Hourly development: estimates, rates and acceptance.
Agree on the accuracy and source of the prices
Determine at which stage the amount is rounded: each item or only the total. Monetary calculations require a defined precision, and the server must recheck the parameters and calculate the result. Changing a number in a browser should not create an order with an arbitrary price. Tariff updates require a responsible person and an effective date.
Continue with: Laravel or a ready-made CMS: when to build a custom app.
Verify the calculation saved with the enquiry
Save the parameters, itemized result and rate version so that the manager can reproduce the result. Check for incorrect units, empty fields, and unavailable combinations. An example of the implementation of the calculator can be viewed in the "Zatyshnyi Dim" case; its business formulas should not be automatically transferred to another project.
Zatyshnyi Dim: website & gate calculator
Is it possible to show only the final amount?
You can, but explaining the included works and exceptions reduces misunderstandings. If the assessment is preliminary, this should be clearly shown next to the result.