How to write an estimate
Write the figure, then write what it assumes. An estimate is a forecast rather than an offer, so the protection for both sides is not the number but the list of things you had to take on trust: quantities you could not measure, conditions you could not see, and work the customer has to do first. An estimate with no assumptions written down is just a price with nothing holding it up.
The Estimate Generator labels the document as an estimate, which is the part people forget. Estimate Generator
Say on the page that it is an estimate
A customer who believes they were given a fixed price treats any increase as a broken promise, however reasonable the reason.
Use the word estimate in the heading and say the figure is approximate. If you already know enough to commit, send a quotation instead: estimating when you could have quoted reads as evasive.
Write down what you could not see
Quantities you assumed rather than measured.
Anything behind a wall, under a floor or inside a system you have not opened.
Materials at today's price, where the price moves.
What the customer has to supply or do first, and what happens to the timeline if it slips.
Tell them before, not after
Almost every dispute about an estimate is about the surprise rather than the money. If the job changes, say so before doing the work and reissue the estimate with the reason next to it.
Some trades work to an informal tolerance of ten or fifteen per cent before a revision is expected. That is a custom rather than a rule, and it is no substitute for telling the customer.
An estimate with a ceiling
If the customer wants certainty and you cannot price the unknowns, offer your best assessment plus a figure you undertake not to exceed without written agreement.
It gives them a number they can budget against without asking you to price guesswork as risk.
Questions people ask next
Is an estimate legally binding?
Generally not in the way a quotation is, because it is presented as an approximation rather than an offer of a fixed price. That protection depends on the document actually reading like an estimate, which is why labelling it matters.
Can I charge more than I estimated?
Usually yes where the extra work was genuinely unforeseen and you told the customer before doing it. What causes disputes is the surprise at the end, not the increase itself.
Should I charge for producing one?
Some trades do where the work needed to produce it is substantial, such as a site survey. If you intend to, say so before you start rather than adding it to the final bill.