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A small extra gets added to the invoice; a big one gets its own quote

You'll come away knowing, with a number decided in advance, whether a mid-project change gets added to the final invoice or needs its own quote, and exactly what to tell the client the moment they ask.

By Yodai · Published on September 6, 2026 · Updated on October 12, 2026

It doesn't matter whether the client took a while to answer or said yes right away: as soon as you start work on that accepted quote, the first surprise shows up. You're halfway through a job and the client texts you: "while you're at it, can you also add...?" It might be a five-minute thing, or it might be half a day more. And you don't know whether that goes on the usual invoice or whether you need to stop and write up a new quote.

If you fold it in without saying anything, two bad things can happen. Either you eat the cost yourself, because you don't dare raise the number you already gave. Or you charge for it at the end without warning, and the client finds out right when it's time to pay, which is the worst possible moment for a surprise.

Does the price change, or does the job change?

The question isn't whether the change looks big or small. It's whether it's still the same job with a small twist, or a different job that's slipped in under the first one.

A custom closet quoted at $640. Halfway through installing it, the client asks to swap the handles on the three doors for pricier ones. That's twenty minutes and three handles from your sample case, already in your van: it's still the same closet, just with one more line on the invoice.

That same client, halfway through, also asks for a matching shoe cabinet for the entryway. That's not a tweak to the closet: it's a new piece of furniture, with its own measurements and its own hours. That doesn't get added to the invoice, it gets its own quote.

The short rule: if you can handle it with what you already have on site and it doesn't change your estimated hours by more than an hour or two, it goes on the final invoice as an extra line. If it means measuring again, buying something you hadn't planned on, or setting aside another day, it's a new job with its own quote.

That one or two hour limit is a rule of thumb, not a law. If you want a reference with a number attached, Spain's Public Sector Contracts Act treats a change as significantly expanding a public contract once it tops 15 percent of the original price, before tax, on construction work, or 10 percent on other contracts. It doesn't bind you, but it gives you a line drawn on paper.

When the extra goes on an individual customer's invoice, charge for the actual time and materials: Spain's General Law for the Protection of Consumers and Users treats it as an unfair practice to round the time worked up, or to charge for things that weren't actually used or consumed.

What you say in the moment, not at the end

The mistake isn't charging for the extra. It's charging for it without saying so. Say it the moment the client asks, with a short phrase you use every time, depending on the case: "we'll add that to today's invoice, it's X dollars more, tax included," or "that's a separate job, I'll send you a new quote in writing." Never "we'll figure it out later" or "don't worry about it."

Saying it in the moment changes how the client takes it. You're not just charging them extra: you're telling them, while they're deciding whether to ask for it, what they'll see on the invoice later. That turns a surprise into their own decision.

And it's not just a matter of good manners. Spain's Civil Code defines taking on a job as carrying it out for a set price. And on a job contracted for a fixed price based on a plan agreed with the owner, it only allows charging more for a change to that plan that adds to the work, and only if the owner has authorized it. If the client is an individual, the consumer protection law also requires you to give them the total price, taxes included, before they're committed. If questions come up later, proving you gave it to them is on you. And if you also work in people's homes in the Madrid region, its home-services decree requires that any change to the quote, whatever it is, be put in writing and approved by the client's signature. It also requires the invoice to match the quote, including any changes.

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