The short answer
An estimate is an educated guess at what work will cost — not binding. A quote is a fixed price offer for defined work — binding once accepted, usually for a stated validity period. An invoice is a request for payment for work delivered — it creates the obligation to pay. Estimate and quote come before the work; the invoice comes after (or at agreed milestones during it).
What is an estimate and when do you send one?
An estimate says "based on what I know today, this will cost roughly X." Send one early, when the client is still scoping and you cannot see the whole job yet — renovations before walls are opened, software before requirements settle. A good estimate states its assumptions ("assumes existing wiring is to code") because the assumptions are what let you re-price honestly when reality differs.
Because estimates are not binding, the worst practice is treating one as a quote under pressure. If the client wants certainty, convert the estimate into a quote — after you have done the diligence that certainty requires.
What is a quote and when is it binding?
A quote is a firm offer: this exact scope for this exact price, valid until a stated date. Once the client accepts, you are committed to the price even if the work takes longer than planned — that is the deal you offered. This is why quotes carry validity windows ("valid 30 days") and explicit scope boundaries, and why anything outside scope becomes a change order at its own price.
In France the devis plays this role and is legally required for many home-services jobs above certain amounts; a signed devis with "bon pour accord" functions as a contract.
What is an invoice and what makes it different?
The invoice is the only one of the three that demands money. It documents what was delivered, references the quote or order it fulfils, applies any taxes, and states a due date. In accounting terms, your invoice creates a receivable for you and a payable for your client; estimates and quotes create neither.
It is also the document with legal formatting requirements — sequential numbering, tax identifiers, mandatory mentions — which vary by country and do not apply to estimates and quotes.
How the three documents flow together
The healthy sequence: estimate while scoping, quote when scope is firm, deposit invoice on acceptance, milestone or final invoice on delivery — each document referencing the previous one. The reference chain ("Invoice for quote Q-2026-014, accepted May 2") is what makes the final invoice unarguable.
In practice the conversion should be mechanical: in InvoiceBirds, an accepted estimate converts to an invoice in one click, keeping the line items, client, and numbering consistent so nothing gets retyped and nothing drifts.
Frequently asked questions
Can an estimate become legally binding?
Generally no — unless your wording or conduct turns it into an offer the client reasonably accepted. Label it "Estimate," state that final pricing may vary, and convert to a quote when you want to commit.
Should I charge for preparing quotes?
For quotes requiring real diligence (site visits, technical scoping), charging a quotation fee creditable against the job is legitimate and increasingly common. For quick quotes, free remains the norm.
Do I send an invoice if a quote was accepted but work is cancelled?
If you have a kill-fee or deposit clause, invoice per that clause. Without one, you can generally only bill work actually performed — which is why cancellation terms belong in every quote.
Put this into practice
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