Estimate, quote or invoice: which is which
The argument that costs a tradesperson money almost always has the same shape. A price was given on a doorstep. The job grew. And nobody wrote down which of three documents that first figure actually was.
Estimate, quote and invoice get used as though they were three words for the same thing. They are not. The difference decides whether you can charge for the extra work or have to absorb it, and it is settled before you pick up a tool, by what you wrote at the top of the page.
An estimate is a considered guess
An estimate says: based on what I can see from here, this is what I expect the job to cost. It is given before anyone has lifted a floorboard, and it carries no promise that the figure survives contact with the joists.
That flexibility is the whole point of an estimate. It is also why an estimate has to say what it is, in one word, at the top. Write Estimate. Then say what it covers and, far more usefully, what it does not.
Say a bathroom is estimated at £4,200. The floor comes up on the Tuesday and two joists are rotten. Replacing them, plus the extra day, comes to £850, so the job finishes at £5,050. That is a fifth more than the customer had in their head, and whether it becomes a bad afternoon depends entirely on one thing: whether the document they are holding says estimate on it, and whether it says anything at all about the floor.
A quote is a promise
A quote is a fixed price. Once the customer accepts it, that is what the job costs, whatever it turns out to involve. In a great many places an accepted quote is a contract, and the person who wrote it carries the risk of having read the job wrong.
None of which is a reason to avoid quoting. Customers prefer a fixed price and will often pay more for one, because you have taken the uncertainty off them and put it on yourself. That is a service. It is worth money.
It is a reason to quote only when you can see the whole job, and to write down the assumptions the price rests on. "Assumes existing pipework is sound" is one line. It is also the line you point at in week three, which is the only week it matters.
Choosing between the two on the doorstep
The honest rule is that you quote what you can see and estimate what you cannot.
A consumer unit change in a flat you have walked round, with the board in front of you and the circuits countable, is a quote. A rewire of a 1930s semi where the previous owner boarded the loft is an estimate, and it stays an estimate until you have been in the loft.
Plenty of jobs are both. Quote the part you can see, estimate the part you cannot, and put the two on the same page under separate headings so the customer understands which half of the number is firm. It reads as competence, because it is.
Which of the two you use is also a decision about who carries the risk of the job running long, and that is worth thinking about separately from how much you can see.The version that gets people into trouble is quoting a job sight unseen because the customer pushed for a figure over the phone. If you have to give one, give a range, and say plainly that it is not a quote until you have looked. A range you revise upward is awkward. A fixed price you revise upward is a dispute.
An invoice is a demand for payment
An invoice comes after the work, or after an agreed stage of it. It is an accounting document rather than a proposal: a number, a date, what is owed, by when, and how to pay it.
It also carries weight the other two do not. Most tax authorities have rules about what an invoice must show and how long you have to keep it. An estimate has no such standing, and you could write one on the back of a delivery note without anybody minding. If a customer needs something to pay a deposit against before any invoice exists, that is a pro forma, and it is not an invoice either. Issue an invoice with a number you have already used, though, and you have a problem with your own records before you have one with the customer.
Label it, then say what it excludes
Two habits close most of the gap, and both take about a minute.
The first is the label. If the document says Estimate, nobody can later insist it was a fixed price, and neither of you is relying on a memory of a conversation in a hallway. The second is the exclusions. Three short lines will do it. Assumes the existing consumer unit is compliant. Decorating not included. Scaffold by others.
Writing down what you are not doing feels like inviting objections. It does the opposite. A customer who reads "scaffold by others" either arranges scaffold or asks you to price it, and both of those happen now, in the quiet part, rather than on the morning the work is supposed to start.
Turning one into the other
The usual sequence is estimate or quote, then acceptance, then invoice. What matters is that the invoice matches what was accepted: the same lines, the same figures, in the same order, with any variation shown separately rather than folded quietly into a bigger total.
Take the bathroom. The invoice reads £4,200 for the work as estimated, then a second line of £850 covering the joists and the extra day, then £5,050. A customer looking at that can see the document they agreed to, plus one clearly marked extra with a reason attached. They pay it.
Now fold the same £850 into the original line and send £5,050 with no explanation. Same money, same work. But the customer's first thought is that they have been overcharged, and their second is to ring you about it.
Where this goes wrong on commercial work
Domestic customers argue with you. Accounts departments do something more expensive: nothing.
A main contractor's system is looking for a match between a purchase order, a delivery of work, and an invoice. If the order says £4,200 and the invoice says £5,050, it does not match, so it stops. Nobody has decided against you. It is simply parked until somebody notices, and that somebody is usually you, three weeks later, on the phone.
The fix is the domestic one done earlier. Get the variation agreed in writing while the joists are still up, ask for the purchase order to be amended, then invoice against the amended figure. An email saying "found two rotten joists, £850 to replace including the extra day, confirming you are happy for me to proceed" is enough. Ninety seconds, and it moves the argument to before the work rather than after the bill.
What to do this week
If the answer is estimate, the next question is whether it is one that gets accepted, which is a separate craft.
Open the last thing you sent a customer. See whether it says, in one word, which of the three it is. If it does not, that is a one line change to your template, and it will go on paying for itself for as long as you are trading.