From an idea to a working quote calculator

Public example: service quote calculator
This is a demonstration brief, not customer work or evidence of generation by QERA.

Outcome: a service business can enter its own assumptions and inspect cost, price before tax and total. The calculation is not a binding quote.
User: a service provider checking a price before offering it to a customer.
Inputs: work hours 0.25 to 500; hourly cost 0 to 10000; materials 0 to 1000000; profit as a percentage of the selling price 0 to 90%; user-selected tax rate 0 to 100%.
Formula: cost = hours × hourly cost + materials. Subtotal = cost / (1 - margin / 100). Tax = subtotal × tax rate / 100. Total = subtotal + tax.
Rounding: round cost, subtotal and tax to two decimals, then add the rounded subtotal and tax.
Example: 4 hours, hourly cost 120, materials 200, margin 20% and tax 0%: cost 680, subtotal 850 and profit 170. Units use the displayed currency; no currency conversion occurs.
Failure states: empty, non-finite and out-of-range inputs show a field error and no valid price. Reset restores the example values.
Scope: public responsive page, Hebrew RTL and English LTR. No account, payment, saved quotes, sending or customer information.
Privacy: calculate locally in the browser. Never track field values. Existing visit analytics depend on site consent.
Acceptance: the example returns 850; zero margin returns cost; 100% margin is rejected; empty input is rejected; tax applies to subtotal; reset, keyboard, copying and mobile layout work.
Assumptions: prices and tax are visitor-replaceable demonstration values, not market rates or a legal tax determination.
Before a real build: decide currency, saved quotes, expiry, customer approval, documents and permissions. Do not silently add them.
Time savings: no measured savings exist for this example. Any estimate must independently separate customer, specification and supplier work, explain assumptions and overlap, and disclose disagreement.