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When I teach my students to write letters, the first question they always ask is: “Do I sound too formal or not formal enough?” It’s a fair question. Letters exist on a spectrum, and the rules that apply to a business letter don’t apply to one you’re sending to a friend. The difference between formal and informal letters isn’t just about tone — it shapes your entire choice of words, structure, and even how you sign off.
I’ll show you how to recognize a formal letter from an informal one, the key differences that matter most, and practical examples you can use the next time you need to write either type. Whether you’re writing to your boss or to your cousin, you’ll know exactly which style to use.
Key Takeaways
- Formal letters are official — they follow a strict format and are sent to organizations, government departments, or people you don’t know personally.
- Informal letters are personal — written to friends and family with a conversational tone and no fixed structure.
- Purpose matters most — formal letters make complaints, requests, or inquiries; informal letters catch up and share stories.
- Structure differs — formal letters have a set layout with name and address blocks; informal letters are freestyle.
- Word choice shows the difference — formal uses “Furthermore” and “Sincerely”; informal uses “Anyway” and “Take care.”
What Are Formal Letters?
A formal letter is a professional written message sent to someone you don’t know well or to an organization. The purpose is usually to make a complaint, request information, apply for a job, or conduct official business. Because the stakes are high, formal letters follow strict rules about structure, language, and tone.
Example 1: Applying for a job requires a formal cover letter sent to the Human Resources department.
Example 2: If you want to dispute a charge on your phone bill, you’d write a formal letter to the company’s customer service department.
Example 3: Requesting a refund or compensation after a poor service calls for a formal complaint letter.
In a formal letter, you don’t relax. Every sentence is deliberate, every word is chosen for impact, and your goal is to create a professional impression that gets results.
What Are Informal Letters?
An informal letter (also called a personal letter) is written to people you know — friends, family, relatives. There’s no business purpose, and there’s no fixed format. The tone is warm, conversational, and personal. You can include slang, colloquialisms, and even emojis if you’re writing via email.
Example 1: A thank-you note to a friend who helped you move house.
Example 2: A letter to your grandmother telling her about your new job and your life.
Example 3: A birthday card to your best friend with inside jokes and casual language.
Informal letters are freestyle. You write how you talk, and the focus is on connecting with the reader, not impressing them.
Side-by-Side Comparison
| Feature | Formal Letter | Informal Letter |
|---|---|---|
| Recipient | Organizations, officials, strangers | Friends, family, close contacts |
| Purpose | Request, complaint, inquiry, application | Catch up, share news, maintain relationship |
| Tone | Professional, respectful, impersonal | Warm, friendly, personal, casual |
| Structure | Fixed format (address, greeting, body, closing) | No fixed format; flexible layout |
| Greeting | “Dear Mr. Smith” or “To whom it may concern” | “Hi Sarah” or “Hey Tom,” or “Dear Mom” |
| Closing | “Yours sincerely” or “Yours truly” | “Take care,” “All the best,” or “Love” |
| Language | Formal vocabulary, no slang, no contractions | Everyday language, contractions, colloquialisms OK |
| Paragraph length | Longer, more structured paragraphs | Shorter, more varied paragraph lengths |
Formal Letter Structure and Format
Formal letters follow a predictable layout. Here’s what you must include:
- Your address — top right, including street, city, postal code.
- Date — one line below your address.
- Recipient’s address — on the left, including their name and title.
- Greeting — “Dear Mr./Ms./Dr. [Last Name]” or “To whom it may concern.”
- Body — 2–4 paragraphs, each with a clear purpose (context, request, closing statement).
- Sign-off — “Yours sincerely,” “Yours faithfully,” or “Regards.”
- Your signature — handwritten or typed name.
Example of a formal letter structure:
123 Oak Street London, UK 15 April 2026 Director of Human Resources ABC Corporation 456 Business Avenue Manchester, UK Dear Mr. Johnson, I am writing to formally request... [Body paragraph with details] [Closing paragraph with call to action] Yours sincerely, [Your name]
Informal Letter Style
Informal letters have no fixed format. You can organize your thoughts however feels natural. What matters is the tone and connection, not the structure.
Example greeting options: “Hi Maria,” “Dear Uncle Tom,” “Hey! How’ve you been?”
Example closing options: “Take care,” “Lots of love,” “All the best,” “Write soon!”
The body can jump from topic to topic. You might tell a story, ask about their life, share gossip, or just ramble. That’s the freedom of informal writing.
Key Differences in Language and Tone
| Aspect | Formal Letter | Informal Letter |
|---|---|---|
| Contractions | Avoid (“I am” not “I’m”) | Use freely (“I’m,” “don’t,” “they’ve”) |
| Vocabulary level | Advanced (“utilize” instead of “use”) | Everyday (“use” instead of “utilize”) |
| Slang | Never | OK and natural |
| Sentences | Longer, complex structures | Shorter, simpler, varied |
| Exclamation marks | Rarely (1 or 0) | Frequently (shows enthusiasm) |
Common Mistakes and How to Fix Them
✗ Incorrect (too casual in formal letter): “Hi John, I’m writing because I wanna complain about my order. It totally sucked.”
✓ Correct: “Dear Mr. John, I am writing to lodge a formal complaint regarding my recent order. It did not meet the expected standards of quality.”
Why: Formal letters require professional vocabulary and tone. Contractions like “I’m” and “wanna,” plus casual phrases like “totally sucked,” undermine your credibility.
✗ Incorrect (too formal in informal letter): “Dear Mother, I hope this letter finds you in good health. The weather in my locale has been inclement of late.”
✓ Correct: “Hi Mom! It’s been raining a lot here, but I’m staying dry. How are you doing?”
Why: Informal letters to family should feel natural and warm, not stiff and distant. Use your actual voice, not an artificial formal one.
✗ Incorrect (mixing styles): “Dear Sir, I’m very upset about my billing issue. Hope we can sort this out ASAP!”
✓ Correct: “Dear Sir or Madam, I am writing to report an error in my recent billing statement. I would appreciate your prompt attention to this matter.”
Why: Once you choose formal style, maintain it throughout. Switching to casual mid-letter makes you look unprofessional.
Sample Dialogue
Emma (student): How do I know which greeting to use? “Dear” seems old-fashioned.
Teacher: Good instinct. “Dear” is standard for formal letters to strangers or officials. It’s not outdated — it’s professional. For informal letters to friends, anything goes: “Hi,” “Hey,” even just their name.
Emma: What about email? Does the same rule apply?
Teacher: Email follows the same logic. Email to your boss? Treat it like a formal letter. Email to your friend? Informal style. The medium doesn’t change the rules — the relationship does.
Quick Quiz
- You’re writing to a company to request a refund. Should your letter be formal or informal?
- You’re thanking your best friend for a birthday gift. What closing would be appropriate: “Yours sincerely” or “Thanks so much”?
- Which greeting is formal: “Hey David” or “Dear Mr. David”?
- In a formal letter, can you use the contraction “I’m” instead of “I am”?
- Your cousin asks for a letter of recommendation for a job. Should it be formal or informal?
Answers: 1. Formal · 2. “Thanks so much” · 3. “Dear Mr. David” · 4. No, avoid contractions in formal letters · 5. Formal (it’s an official document).
Related Articles
- How to Write a Formal Letter in English
- How to Write Informal Letters in English
- ↑ Back to pillar: English Writing Guide (Pillar)
Frequently Asked Questions
What is the main difference between formal and informal letters?
The main difference is purpose and relationship. Formal letters are sent to strangers or organizations for official reasons (complaints, requests, applications) using professional language and a set structure. Informal letters are sent to friends and family with a warm, conversational tone and no fixed format.
Can I use contractions in a formal letter?
No. Formal letters require full forms: write “I am” instead of “I’m,” “do not” instead of “don’t,” and “cannot” instead of “can’t.” Contractions make formal writing appear casual and less professional.
What is the correct greeting for a formal letter?
Use “Dear Mr./Ms./Dr. [Last Name]” if you know the recipient’s name. If you don’t know their name, use “To whom it may concern” or “Dear Sir or Madam.” Avoid casual greetings like “Hi” or “Hey” in formal letters.
How long should an informal letter be?
There’s no set length for informal letters. They can be a short note or several pages long. Write until you’ve said what you want to say. The tone and content matter more than length.
Is it OK to use slang in an informal letter?
Yes, slang is perfectly acceptable in informal letters to friends and family. In fact, using your natural voice — including slang — makes the letter feel more genuine and personal. Just avoid slang in formal or professional contexts.
How do I close a formal letter?
End with a formal closing such as “Yours sincerely,” “Yours faithfully,” “Regards,” or “Respectfully.” Then sign your full name. Never use casual closings like “Take care” or “All the best” in formal business letters.
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