Cheques and contracts
The main reason to write a number in words is that it cannot be altered afterwards. A figure can gain a zero; four thousand two hundred cannot. That is why cheques carry both, and why contracts often repeat a sum in words after the numerals.
Cheque style has its own conventions: the amount, then and, then the pence or cents as a fraction over 100, then a line to the end so nothing can be added.
British and American differ
British usage inserts and before the tens: one hundred and twenty-three. American usage omits it: one hundred twenty-three. Both are correct in their own place, and mixing them in a legal document looks careless.
Above a million the two systems used to disagree about what a billion was. Both now use the short scale, so a billion is a thousand million everywhere in English — but older British documents may not mean that.
Frequently asked questions
Which style should I use on a cheque?
The one your bank’s country uses. British style includes "and" before the tens; American style omits it. Both are shown.
How are pence or cents written?
As a fraction over 100 after the word "and" — the convention on cheques, because it cannot be extended.
How large a number can it handle?
Into the quadrillions. Beyond that the names stop being standard enough to be useful.
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