A client asks what the job will cost. You send a number. Months later the work has grown, your final invoice is higher than that number, and the client is pointing at the document you sent saying they agreed to a price. Whether they are right depends almost entirely on which document you actually sent — and, more often than not, on whether you were clear about it at the time.
Estimates and quotes are not interchangeable words for the same thing. One is a forecast that can move; the other is a commitment that generally cannot. Using the wrong term, or using neither and just sending "a number", is how pricing disputes start.
The difference in one line each
An estimate is your best assessment of what the work will cost, given what you know now. It carries an implicit "approximately". It is appropriate when the scope genuinely cannot be pinned down in advance — remedial work where you cannot see behind the wall, open-ended consulting, anything billed by time where the hours depend on what you find.
A quote is a fixed price for a defined scope. Once the client accepts it, you have agreed to do that work for that money. If it takes twice as long as you thought, that is your problem — which is precisely why a quote should only ever be given against a scope you have properly understood.
The commercial consequence follows directly. An estimate transfers risk to the client, who does not know the final number. A quote transfers risk to you, who has fixed the number before doing the work. Clients naturally prefer quotes; that preference is exactly why quoting badly is expensive.
| Estimate | Quote | |
|---|---|---|
| What it says | This is roughly what it should cost | This is what it will cost |
| Binding on price | No — it is a forecast | Generally yes, once accepted |
| Who carries the risk of overrun | The client | You |
| Scope needs to be | Broadly understood | Fully defined |
| Best for | Time-based or exploratory work | Well-defined deliverables |
| Final invoice | May differ from the figure | Should match the figure |
What makes a quote binding
A quote generally becomes contractually binding when the client accepts it, because that is the point at which an offer meets acceptance. What binds is the price *for the scope described* — which is why the scope description, not the number, is the part worth labouring over.
Three things protect a quote without weakening it. State exactly what is included, in enough detail that a reasonable person could tell whether a given task falls inside or outside it. State what is excluded, especially the obvious-to-you things a client might assume are covered. And give the quote an expiry date, so that a price based on today’s material costs or today’s availability does not get accepted six months later.
None of this makes a quote unchangeable. It means changes go through a variation: the client asks for something outside the stated scope, you price it, they agree, and the additional amount is documented before the work happens. A quote plus documented variations is a defensible final invoice. A quote plus unannounced extras is an argument.
When an estimate is the honest answer
There is a temptation to quote everything because clients like certainty. Resist it where the uncertainty is real. Quoting a fixed price for work whose scope you cannot see is not confidence, it is gambling — and the usual outcome is either a loss you absorb or a difficult conversation you could have avoided by being straight at the outset.
A good estimate does more work than a bad quote. Give a range rather than a single figure, because a range communicates the uncertainty honestly. Say what the number assumes, since the assumptions are what will move it. Explain what would push it toward the top of the range. And commit to telling the client before you exceed it, which is the single thing that turns an estimate from a source of disputes into a source of trust.
A common and sensible hybrid: estimate the discovery phase, then quote the delivery once discovery has told you what the work actually is. The client gets certainty where certainty is possible and honesty where it is not.
Where these sit in the document chain
Estimates and quotes both live before the work, and neither is a request for payment. Nothing is owed on the strength of a quote alone — it is an offer, and until the work is done and invoiced there is nothing to pay.
The sequence in most jobs runs: estimate or quote, then acceptance (a signature, a purchase order, or a clear written yes), then the work, then the invoice, then the receipt. Each document does one job. The invoice is the only one that demands money, which is why it is the only one carrying payment terms and a due date.
One neighbour causes regular confusion: the proforma invoice. It looks like an invoice, but like a quote it precedes the transaction being booked and does not demand payment as a debt — it is commonly used so a buyer can raise a purchase order or arrange funds. If you need a document that resembles an invoice but is not yet one, that is usually the right choice rather than an "invoice" you did not mean literally.
Common Mistakes
Using the words interchangeably
Saying "here is my estimate" and then treating it as a fixed price — or the reverse — is where most disputes begin. Label the document explicitly, and if a client refers to your estimate as a quote, correct it in writing at the time rather than after the invoice.
Quoting a price without defining the scope
A number with no scope attached is unenforceable in your favour and infinitely stretchable in the client’s. The scope description is the part of a quote that protects you; the price is just the consequence of it.
Letting quotes live forever
Without an expiry date, a quote priced against last year’s costs can be accepted today. Thirty days is a common and defensible validity period, stated on the document itself.
Doing extra work before agreeing the extra price
Once the work is done, your leverage is gone and the conversation becomes a request for goodwill. Price the variation, get a written yes, then start.
Frequently Asked Questions
Is a quote legally binding?
Once the client accepts it, generally yes — it functions as an offer that acceptance turns into an agreement on price for the scope described. That is why the scope wording matters more than the number, and why an expiry date is worth including.
Can I charge more than my estimate?
Usually yes, since an estimate is a forecast rather than a commitment — but "legally permitted" and "commercially wise" differ. Tell the client before you exceed the figure, not on the invoice. An unexpected overrun discovered at billing time is the fastest route to a dispute or a discount.
Do I need to send a quote at all?
Not always, but sending something written is almost always worth the few minutes. Verbal pricing leaves you with no record of what was agreed, and memory reliably favours whoever is paying.
What is the difference between a quote and a proforma invoice?
A quote offers a price for work not yet agreed. A proforma invoice usually comes after agreement and presents the transaction in invoice form — commonly so the buyer can raise a purchase order or arrange payment — without being a demand for a debt. Neither is a real invoice, and neither should be entered into your books as revenue.
Sources & Further Reading
- Invoicing and taking payment from customers — GOV.UK
- Payments and invoicing for business — business.gov.au, Australian Government
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