The difference in one line
An estimate is an informed prediction of cost. A quotation is a fixed price. An invoice is a request for payment. The word you use tells the customer how much they can rely on the number.
| Feature | Estimate | Quotation | Invoice |
|---|---|---|---|
| Says | Roughly this much | Exactly this much | Pay this much |
| Can change | Yes, within reason | Not without agreement | Only via a credit note |
| Given when | Scope is not fully known | Scope is clear | Work is done |
| Key date | Date prepared | Valid until | Due date |
| Typical use | Repairs, diagnostics, renovation | Defined supply or project | Every completed sale |
When an estimate is the honest answer
Some work genuinely cannot be priced in advance. A leak behind a wall, a fault in an old installation, a renovation where nobody knows what is under the floor. Giving a fixed quotation for work you cannot yet see means either padding the price heavily or absorbing the risk yourself.
The professional move is to say so: give an estimate, explain what would change it, and offer a fixed price once the diagnostic stage is complete.
How to write an estimate that will not cause an argument
Label it clearly
The word ESTIMATE at the top. Not “quote” in the covering email and “estimate” on the document.
State the assumptions
What you have assumed about access, condition, materials and quantities.
Give a range if the uncertainty is real
A range with an explanation is more honest and more credible than a precise-looking single figure.
Say what would change it
“If the joists are affected, add approximately X.”
Agree a variation threshold
Commit to contacting the customer before exceeding the estimate by more than an agreed percentage. This is the single most effective clause for avoiding a disputed final bill.
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Invoicing after an estimate
The final invoice should show clearly how it relates to the estimate:
- Reference the estimate number and date.
- Keep the same line structure so the two can be compared side by side.
- Put anything additional on its own line, with the date it was authorised.
- If the total exceeds the estimate, explain why on the document — not only in the covering email, which will not be filed with it.
A customer who was told “about $800” and receives an invoice for $1,150 will remember the first number. Whether that becomes a dispute depends entirely on whether the increase was flagged before you did the work.
Several countries limit how far a final bill may exceed an estimate given to a consumer, or require prior authorisation above a threshold. Check what applies where you trade before relying on your own terms.
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Questions
Is an estimate legally binding?
Generally it is not a fixed price in the way a quotation is, but it is not meaningless either — a final bill far above an estimate can be challenged, and some jurisdictions regulate the gap for consumers. Label the document accurately and flag changes before doing the work.
How much can a final invoice exceed an estimate?
There is no universal figure, and some countries set rules for consumer work. The practical answer is: however much you agreed in advance. Set a threshold at which you will contact the customer, and honour it.
Should I charge for producing an estimate?
Charging for the diagnostic work behind an estimate is reasonable and common in trades — often credited against the job if it proceeds. Say so before you attend.
Can an estimate become a quotation?
Yes, and it often should. Once the diagnostic stage tells you what the job involves, issue a fixed quotation for the remaining work.
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