Is the suffix dot in "Mr." optional or required?

Question

I am pretty sure I am aware of the meaning of "Mr.", which is a title used before the family name or full name in of a man who has no other title, or when talking to man who holds a particular official position.

source: Cambridge Dictionary

However, the usage of "Mr." or "Mr" confuses me a bit, that is whether the suffix dot "." in "Mr." is optional or required.

I see both two forms are commonly used, Google Ngram shows that the former is more commonly used than the latter.

even Cambridge Dictionary uses both of them.

Good afternoon, Mr Dawson.

I’m afraid I can’t agree with what’s just been said, Mr. Chairman

Is it a matter of AmE vs. BrE or just something about style?

Answer 1

Purely style. In British use the dot is usually omitted. In American use the dot is usually included.

But unless you are required to follow a particular style guide, it doesn't matter. Do try to be consistent.

British usage favours omitting the full stop in abbreviations which include the first and last letters of a single word, such as Mr, Mrs, Ms, Dr and St; American usage prefers (A) Mr., Mrs., Ms., Dr. and St., with full stops.

http://www.sussex.ac.uk/informatics/punctuation/capsandabbr/abbr

Answer 2

Should you write Mr Smith or Mr. Smith? Should you write Dr Jones or Dr. Jones?

If you're following US convention, put a period (full stop) after your contraction.

If you're following UK convention, you have a choice whether to use a full stop (period) or not.

Here's a useful guideline for Brits:

If the last letter of a contraction is the same as the last letter of the whole word, then don't use a full stop (period).

For example: Mister -> Mr
(The last letters are the same.)

Professor > Prof. (The last letters are different.)

This link might be helpful: https://www.dailywritingtips.com/does-mr-take-a-period/