An estimate and a quote are two different promises

The same number can mean two things

A figure given to a client is not simply a figure. It carries an implication about how firm it is, and the two common words for it carry different implications. Broadly, a quote is understood as a price the seller is committing to, and an estimate as a considered prediction that may move.

Exactly how much weight each word carries in law differs between countries and depends on what else was said and written, so nothing here should be taken as a statement of your legal position. What is universal is the expectation gap: the client heard a number, and if the final bill is different they will refer back to how it was described.

Why an estimate is sometimes the honest instrument

A fixed price requires a scope that can actually be fixed. Where the work involves opening something up, working with materials whose condition is unknown, or responding to what is found along the way, a firm number is not confidence; it is a bet, and the seller is the one placing it.

In that situation an estimate is more accurate rather than less committed. It tells the client the truth — this is what jobs like this usually come to, and here is what would make it more — instead of quoting a fixed price with a hidden contingency inside it that the client pays for even when nothing goes wrong.

An estimate still needs a basis

The failure mode of estimates is vagueness. A number with no explanation attached is treated by the client exactly as a quote would be, and the fact that you called it an estimate won’t save the conversation when the invoice arrives.

A usable estimate says what it assumes: the quantities expected, the condition of what you will be working on, what the client is providing, and how long it should take. Those assumptions are what make a change explicable later. When the assumption turns out to be wrong, you are not asking for more money; you are pointing at the sentence that said this figure depended on something that has turned out differently.

And a mechanism for the number moving

Alongside the assumptions, say how a change will be handled. The useful pattern is a threshold and a pause: below a stated amount you proceed and it appears on the invoice, above it you stop and get agreement first.

That single arrangement prevents nearly every serious argument about a final bill, because it converts an unpleasant surprise into a decision the client made at the time. It also protects you, since a client who approved the extra work in writing has considerably less room to dispute it afterwards.

The moment to raise it is the moment you know

People delay this conversation because it is uncomfortable, and delay is what turns a manageable adjustment into a serious dispute. A client told on Tuesday that the job will cost more has options: approve it, change the specification, or stop. The same client told at the end has only the option of arguing.

The delay also damages your credibility on everything else. A supplier who reports a problem promptly reads as someone paying attention. The same supplier reporting it three weeks late reads as someone who hoped it would go away, which is a different and less reassuring impression.

Choose deliberately and say which it is

Fixed prices suit work you have done many times, with a scope you can define and control. Estimates suit work with genuine unknowns that the client is better placed to accept than you are. Both are legitimate, and the failure is not choosing — writing a number in an email with no indication of which kind of promise it represents.

Whichever you use, use the word, and use it consistently in the document, in conversation and on the invoice. It costs one sentence, and it is the sentence you will want to have written when somebody queries the total nine weeks later.

It is also worth putting an expiry on either kind of number. Costs move, your diary fills, and a figure given in March should not still be binding in October because somebody kept the email. A stated validity period is standard practice, nobody objects to it, and it removes an argument you would otherwise have entirely on the client’s terms.