Here we have given formal and informal letter difference which will help to understand basic difference between formal and informal letter.
| Formal Letter | Informal Letter |
| It is written in a formal way or a professional way | It can be casual also |
| It is an official announcement by a person or a firm | It is non-official |
| The format of the letter should be followed | There is no particular format |
| They are written for official reasons | They are written for personal reasons |