# "and" in number composition

I'm learning number, big numbers like one hundred (100) or one thousand (1000).

The question is: for a composed number e.g. 73,987, that I can write as,
seventy-three thousand, nine hundred and eighty-seven

Is the and word mandatory?
or can I simply write seventy-three thousand, nine hundred eighty-seven

another example: 123,601,
one hundred twenty-three thousand, six hundred one
one hundred and twenty-three thousand, six hundred and one

And if there are differences between British and American English.

In formal usage in American English, "and" is reserved to introduce fractional values, and using it anywhere else in the number is discouraged. So, the short answer to your question in American English is that not only do you not have to put any of those "ands" in there, but people who are finicky about how numbers should be spoken will love you for leaving it out.

However, if you want to know more about where it can and can't be used in common speech, read on. People often use it before whichever spoken number sounds like it is the last in the list. For example, these are all common:

one hundred and one
one thousand and ten
four thousand and twenty-two
one-hundred-and-twelve thousand

However, it's unusual to use it before the hundreds place. This sounds a little weird:

three thousand and seven hundred

It's also unusual to use it between the million and thousands places or the billions and millions places. These all sound weird, too:

one million and nine hundred thousand
one million and fifty thousand
one million and two thousand
one billion and six million

But using "and" is okay between these large numbers and the tens or ones places:

three million and twelve
one billion and six
• Comments are not for extended discussion; this conversation has been moved to chat. Feb 12 '18 at 23:27

In British English and is usual, and omitting it is strange.

In American English, it is common to omit it. I don't know whether they sometimes include it.

• It’s included sometimes, and omitted sometimes. Insofar as spoken language goes, I wouldn’t even venture a guess as to which is more common.
– J.R.
Feb 11 '18 at 21:00
• Formally (like when writing a check) we leave it out. Informally, we probably use it as often as leave it out. Feb 11 '18 at 23:49
• [...] usual [...] isn't enough. Can you extend your answer for British English? Feb 12 '18 at 21:30
• I disagree. In AmE, I often have to write large dollar or currency amounts and I always put an and in at the end when the number must be written out in a text (law, contracts, etc.). Also, in dialogues or literary writing, you would say and. "The family had a mere three hundred and twenty dollars to its name." Feb 12 '18 at 21:59