An estimate supports a decision
An estimate or quotation describes work the business is prepared to provide. It can include line items, quantities, taxes, discounts, notes, photographs, expected terms and an acceptance period.
Because the customer is still deciding, the document should distinguish included work from optional work. It should also identify assumptions that could require a revised scope after inspection or selection.
An invoice records what is being billed
An invoice identifies the customer, the billed items, the invoice date, payment terms, total, recorded payments and remaining balance. It may represent the full approved job or a defined stage, depending on the actual agreement.
An invoice should not be used to quietly introduce work the customer did not approve. Where added work changes the agreement, document that scope before incorporating the approved amount into billing.
Conversion preserves useful details
Converting an accepted quotation into an invoice reduces repeated data entry and keeps the customer, line items, prices, taxes and notes connected. Review the resulting invoice because dates, due terms or final quantities may still require attention.
Retain the original quotation as part of the customer history. It explains what was proposed, while the invoice explains what is being charged and what remains outstanding.
Changes belong in a visible record
A project rarely becomes clearer when the original approved document is overwritten. Use a separate change record when a customer adds, removes or substitutes work, especially when price or schedule changes.
The practical objective is traceability: a customer should be able to follow the proposal, approval, changes, invoice and payments without comparing unrelated files or message threads.
This practical information is general and is not legal, accounting or tax advice. Review requirements that apply to your business and location.