Quote vs Invoice — What's the Difference and When to Send Each

Quotes and invoices sit at opposite ends of the same transaction. One asks for a decision; the other asks for money. Sending the wrong one is not just a paperwork error — it changes what you are asking the other party to do, and in some cases what you have committed yourself to.

The short version

	Quote	Invoice
Sent	Before the work	After the work
Purpose	Offer a price	Request payment
Asks for	A decision	Money
Amounts	Proposed	Owed
Expires	Yes — state a date	No, but has a due date
In your accounts	Not recorded as revenue	Recorded as revenue
Numbering	Its own sequence	Gap-free, sequential
If it is wrong	Reissue it	Issue a credit note

That last row is the one people discover late. A quote can be withdrawn and replaced freely, because nothing has happened yet. An invoice cannot — it is part of a numbered record, and correcting it means cancelling it formally.

What a quote does

A quote is an offer. It says: here is what I will do, here is what it costs, and here is how long that price stands.

The validity period is the part people skip, and it is the part that protects you. Without an expiry date, a client can accept a six-month-old quote at prices that no longer cover your costs — and in many jurisdictions that acceptance is binding, because you made an offer and they took it. Thirty days is the usual default. Use less if your input costs move quickly, and say so plainly: "This quote is valid until 5 September 2026."

Three other things earn their place on a quote:

• What is not included. Scope disputes almost always trace back to an assumption nobody wrote down. A short exclusions list costs two minutes and settles arguments that would otherwise cost days.
• What happens if the scope changes. Not a threat — a process. "Additional work is quoted separately before it starts" tells a client how change is handled, which is reassuring rather than alarming.
• Your payment terms. This is the moment they are agreed. Terms that appear for the first time on the invoice have not been agreed at all; they have been announced.

What an invoice does

An invoice is a demand for payment for work already delivered. It is a financial record: it enters your books as revenue, it enters your client's as a payable, and it is the document a tax authority will want to see if it ever asks.

Because it is a financial record, an invoice needs things a quote does not — a unique, gap-free number, a payment due date as an actual date, and your tax registration details where you have them. The full field list is in how to create an invoice.

An invoice is also not a contract, which surprises people. It is evidence of a transaction, read alongside whatever you actually agreed. It cannot impose a term the client never accepted — one more reason the terms belong on the quote.

The order of operations

1. Quote — you offer a price. The client decides.
2. Acceptance — ideally in writing. An email saying "yes, go ahead" is fine, and is worth more than a phone call you both remember differently.
3. (Optional) Purchase order — larger clients issue one to authorise the spend internally. Put its number on your invoice or payment may never be released.
4. You do the work.
5. Invoice — you request payment, mirroring the accepted quote.
6. Receipt — you confirm the payment arrived.

Skipping step two is the expensive one. Work started on a verbal "sounds good" is work you may struggle to invoice for, because the thing you would point at in a disagreement does not exist.

Step three quietly costs the most time. A purchase order is not bureaucracy for its own sake — in many finance systems it is the authorisation, and an invoice arriving without a matching PO number is not rejected so much as parked. Nobody writes to tell you. Ask at acceptance whether a PO will be raised, and if so, wait for the number before invoicing.

Where a proforma invoice fits

A proforma invoice is the confusing middle case. It looks like an invoice but functions like a quote: it states a committed price before delivery, and it is not a demand for payment or a revenue entry.

It exists because some buyers need an invoice-shaped document to release an advance payment, arrange financing, or clear customs. If a client asks for "an invoice so we can pay a deposit", a proforma invoice is usually what they actually want — sending a real invoice would put revenue in your books for work you have not done, in a tax period it does not belong to.

The exception is when they genuinely intend to pay against it now. If you are asking to be paid a deposit, that is a real invoice for a real amount, recorded as such, and deducted on the final invoice at the end. The test is simple: are you asking for money today, or telling them what the money will be?

Estimate, quote, or tender?

These get used interchangeably, and the difference is how firm the number is:

• An estimate is an approximation and is expected to move.
• A quote is a fixed price you commit to.
• A tender is a formal quote submitted in a competitive process, usually against a specification you did not write and cannot vary.

Say which one you are sending, in the document, in the first line. The word does real work: it sets what the client believes they are holding, and that belief is what they will argue from later.

If you genuinely cannot fix a price — because the scope depends on what you find — an estimate with a stated range and a trigger for re-quoting is more honest than a fixed price you intend to revise. "Estimated at £3,000–£4,000; I will confirm a fixed price after the first week" is a sentence clients accept far more readily than an unexplained overrun.

Writing a quote that gets accepted

The document does more of the selling than most people expect, because it is usually the thing forwarded to whoever actually approves the spend — somebody who was not in the conversation and will read it cold.

Four things make that reader's job easier:

• Lead with what they get, not what you do. "Website performance audit and a prioritised fix list" is a deliverable. "20 hours of consultancy" is a timesheet, and a timesheet invites negotiation about the hours.
• Break the price down, but not too far. Three to six lines is the range where a client can see what they are paying for without being handed a menu to cut items from. One undifferentiated total invites "can you do it for less?" with nothing to discuss.
• Offer options rather than one number, where it fits. Two or three scopes at different prices changes the question from whether to which. It also gives a budget-constrained client a way to say yes to something.
• Put the next step at the bottom. "Reply to this email to accept and I will book the week of the 14th" converts far better than a document that simply stops.

Following up on a quote

Almost nobody does this, and it is the cheapest win available.

A quote that goes unanswered has usually not been rejected. It has been read, filed for a decision that needs somebody else, and forgotten. One short note a few days later — not a chase, a genuine offer to help — recovers a meaningful share of them.

The useful version asks a question rather than repeating the price: is the scope right, is the timing right, is there anything they need for an internal approval? Each of those gives them something easy to reply to, and the answers tell you whether to revise the quote or move on.

The expiry date does the rest of the work. A quote that says "valid until 5 September" creates a natural reason to follow up on the 3rd that is not pressure — it is a fact about the document.

When a quote lapses or changes

If a quote expires without acceptance, do not simply honour it out of politeness when the client returns two months later. Reissue it, with today's date, today's prices and a new validity period. That is not awkward — it is what the expiry date was for, and clients who work with quotes expect it.

If the scope changes before acceptance, issue a new quote with a new number and say plainly that it supersedes the previous one. Amending a sent quote in place leaves two documents with the same reference and different contents, which is the same problem gap-free invoice numbering exists to prevent — just with lower stakes.

If the scope changes after acceptance, that is not a quote revision. That is additional work, quoted separately, approved separately, and shown as its own line on the final invoice. The moment you fold extra work silently into an existing price is the moment the invoice stops matching the quote.

Making the invoice match the quote

The practical trick is that the invoice should be a continuation of the quote, not a fresh document that has to be reconciled against it.

If the quote said £4,200 across six lines, the invoice should say £4,200 across the same six lines, in the same order, using the same words. Every unexplained difference is a reason for somebody to pause and ask a question, and every question is days.

Where the final figure genuinely differs, show why on the invoice rather than leaving it to be discovered:

• Extra work should appear as its own line, described as extra, ideally referencing the approval.
• A deposit already paid should appear as a deduction, not as a silently reduced total.
• A discount should be a line, not a quietly rounded-down subtotal.

An invoice that explains its own arithmetic gets approved by one person. One that does not gets forwarded.

The quote generator and invoice generator share the same line-item structure for exactly this reason, and an accepted quote can be carried straight over rather than retyped — which removes the transcription errors that create the discrepancies in the first place.

What to keep, and for how long

Invoices are the records with a statutory retention period, and it is commonly several years — the exact figure depends on where you are registered, so check rather than assume.

Quotes have no such requirement, and they are still worth keeping. An accepted quote is the closest thing many small engagements have to a contract, and it is the document that answers "was that in scope?" when the question arrives eight months later. Keep the version the client accepted, not just the last one you edited.

Getting both right

Send a quote before the work, with an expiry date and an exclusions list. Get acceptance in writing. Ask about a purchase order. Do the work. Then send an invoice that mirrors the quote, prints an actual due date, and explains any difference on its face.

None of that is complicated. It is a sequence — and most payment problems are what happens when one step of it gets skipped because everybody was being agreeable.