A claim letter is not a legal document and does not need to sound like one. It needs to contain the handful of facts that let somebody at the airline look your flight up, decide the question and pay it, and it needs to be specific enough that a vague refusal is obviously a vague refusal. Writing it yourself costs nothing, which is worth saying plainly on a page that also links to a company that would charge you a share of the money.
The six facts, and nothing else
Give the booking reference, the flight number and date, the scheduled and actual arrival times at your final destination, the number of passengers on the booking and their names, the sum you say is due with the distance band you have used, and the bank details for payment. Everything else is decoration. Do not describe the inconvenience: neither instrument prices it, and a letter that spends three paragraphs on a missed birthday and one line on the arrival time is harder to process, not more persuasive.
Cite the article, and say what it says
Name the provision you rely on and quote the sentence rather than characterising it. For a long delay under the retained UK Regulation that is the article giving a right to compensation where the passenger reaches the final destination three hours or more late, read with the article that sets the distance bands. A quotation with a link is checkable by whoever opens your letter, and it moves the conversation from what you believe you are owed to what the instrument says, which is the ground you want to be arguing on.
Anticipate the extraordinary-circumstances answer
The most common reply is a paragraph naming a cause and asserting that it was outside the airline's control. Ask for two things in the same letter so the refusal has to engage: the specific reason for the delay to your flight, and the reasonable measures the airline says it took to avoid it. The Regulation puts both halves on the carrier, so asking for them is asking it to make out its own defence. A reply that names weather and stops has not done that, and an ADR scheme can be told so.
What to do with the answer, and what it costs
If the airline pays, you are done. If it refuses or does not reply, the next step is free: the Alternative Dispute Resolution scheme the airline belongs to, or the Civil Aviation Authority's own complaints route where it belongs to none. A US carrier must acknowledge a written complaint within thirty days and send a substantive reply within sixty. A claims company is a paid alternative that takes a share of whatever it recovers; it is a convenience for people who would rather not do any of this, and never a requirement.
Questions people ask about flight delay compensation letter
Do I need a template?
No. A short letter containing the booking reference, the flight number and date, the actual and scheduled arrival times, the passengers, the sum claimed and your bank details will be processed the same as anything longer.
Should I write to the airline or use a claims company?
Writing direct costs nothing and the free escalation routes after it also cost nothing. A claims company keeps a share of what it recovers. If you use the one linked from this site we are paid a commission by it, which is why the link is marked as paid and is not offered first.
What if the airline ignores me?
Silence is treated as a refusal by the free escalation routes. In the United Kingdom take it to the airline's ADR scheme, or to the Civil Aviation Authority where the airline belongs to no scheme.
How far back can I claim?
The Regulation sets no limitation period of its own; the deadline comes from the general law where you bring the claim, and in the United Kingdom it is counted in years. Do not assume an old flight is out of time without checking.