What do we call three parts of a month?

[bigC]

There are 30 days in September, we call the period 11th-20th September "Mid-September".

What do we call the period 1st-10th September, and the period 21st -30th September?

[GoesStation]

None of these terms are that precise, but you can divide a month into (for example) early September, mid-September, and late September. Note that only mid-September takes a hyphen as a noun phrase. They're all hyphenated when they're adjectives: It was a late-September evening.

[Tarheel]

This one.

[bigC]

None of these terms are that precise, but you can divide a month into (for example) early September, mid-September, and late September. Note that only mid-September takes a hyphen as a noun phrase. They're all hyphenated when they're adjectives: It was a late-September evening.

Are "early, "mid" and "late" also applicable to year?

[tedmc]

You can divide the year into four quarters and call them first quarter (1Q), second quarter (2Q) and so on, as is common in business reports.

[Rover_KE]

Are "early, "mid" and "late" also applicable to a year?

Yes, but Ted's answer is better.

Note that I have improved your thread title. We don't start a question with 'How to', and it should have had a question mark anyway.

[Piscean]

'Mid-year' is not uncommon.

[Rover_KE]

This one.

?

[Tarheel]

?

I was suggesting "What to call the parts of a month" instead of "How to ...."

[Charlie Bernstein]

Are "early, "mid-" and "late" also applicable to year?

I think they're fine. We don't always need to be exact.

Note, though, that mid isn't a word, it's a prefix. So it's hyphenated, and it's sometimes phrased differently. Examples:

- It was early/late 2010 when we met.
- It was mid-2010 when we met.

- I'll see you sometime early/late in the year.
- I'll see you sometime mid-year.