I have a similar question to the one below When writing out large numbers in words, should commas be placed at thousand separators?
I'm writing a program to spell out large numbers, and am unsure if there should be a comma or an "and" in the following numerals, before the "24":
101024 "One hundred and one thousand, and twenty-four"
1024 "One thousand and twenty-four"
I think that this is rarely a problem in real life, but what would be the correct way of doing this?
Not clear whether the questioner wants British or American usage: the British normally use and before the tens position, as in the original example.
The additional examples given in OldPro's answer would in British English be:
"Twelve thousand one hundred and twenty point two four" (since there's no currency sign, the decimals should not be assumed to be cents, but £12,120.24 would be read as "Twelve thousand one hundred and twenty pounds and twentyfour pence" (on a cheque I would also spell out the main currency like this, but follow it with the minor denomination in figures, e.g. "...pounds 24" unless it is zero, in which case I would write a long dash).
"Two million fifty-four thousand nine hundred and ninety-nine"
I would not normally use commas, but that's just a matter of personal choice. Just make sure that the addition of a comma cannot change the meaning (especially on a cheque).
Although not directly related to the placement of commas when writing large numbers in words, I would like to point out that many non-English speaking countries (I'm thinking primarily of European countries, as I can't vouch for others) use the comma to denote the decimal point when writing out digits. They also use spaces instead of commas to break the digits into groups of three (as @EdwinAshworth has illustrated).
So, while not advocating using commas as decimal points, I would advocate - depending on the likely audience - avoiding the use of commas entirely when writing large numbers in digits so as to avoid possible confusion by some readers, for example (using Edwin Ashworth's illustration):
use 101 024 instead of 101,024 because some readers may read the latter as one hundred & one point zero two four.
I state without much authority that commas are placed similarly to numerals at the thousands, millions, and billions marks, and that "and" is only used at the decimal point. It's just how I've seen it done on checks where it is required to spell out the amount.
101024 "One hundred and one thousand, twenty-four"
1024 "One thousand, twenty-four"
12120.24 "Twelve thousand, one hundred twenty and twenty four cents"
2,054,999 "Two millon, fifty-four thousand, nine hundred ninety-nine"
I think using "and" other than for the decimal point detracts from readability. Commas are much more debatable but it makes some sort of sense to put them where I say in that it means that the numbers spelled out between commas never reach into the thousands.
I don't think a bank handling an account with that amount of money in it is likely to be too captious.
"One hundred and one thousand and twenty-four" and "One hundred and one thousand, and twenty-four" are both (if we know we're dealing with numbers rather than additions), unmistakably, spelt-out forms of 101 024 (which is how we taught kids to write longer numbers; we were taught 101,024 in my day).
Since neither leads to interpretational confusion, it becomes a style choice (as with 101 024 rather than 101,024). Is the comma'd version
a) easier on the brain
b) easier on the eye
c) easier on the reader-out?
