Money in words

An amount is split at the decimal point as text and the cents are counted as a whole number of cents from there on. It never becomes a decimal fraction on the way through. That matters because, in the arithmetic almost every computer uses, 4.35 multiplied by a hundred is 434.99999999999994, and a converter that takes the whole part of that prints thirty-four cents on an invoice for thirty-five.

One decimal place is read as tens of cents, so 1500.5 is fifty cents rather than five. Three or more decimal places are refused, because rounding them would change the amount you typed.

An amount below one unit is written as its cents alone, as it is on a document: fifty cents, not zero rand and fifty cents.

The fraction. On a cheque in the United States the cents can be written as a fraction of a hundred: one hundred twenty-five and 50/100 dollars. The FDIC's guide to writing a cheque, Money Smart, puts it this way: “Spell out the dollars – like ‘seventy eight.’ Then put the cents as a fraction of one hundred, like 23 one hundredths. Again, this prevents anyone from changing the amount of the check.” It is a banking convention, so it is offered as an option and is never the default. With it, the cents are always two digits, 00/100 when there are none, and the currency comes last.

Capitals. UPPERCASE sets the whole line in capitals, for a form that asks for block letters. Title Case capitalises every word, and both halves of a hyphenated number, except “and”: One Hundred and Twenty-Five Dollars and Fifty Cents Only. The capitals change nothing about the amount, and the words and figures checker reads every one of these forms.

Every currency here is counted in thousands and millions and divided into a hundred of a smaller unit. The unit names are given in full, including the plurals that adding an s gets wrong: rand, naira and kobo take no plural, fils does not change either, and a pound has one penny but fifty pence.

The Indian rupee is not included yet. Indian English counts in lakh and crore, and the tools here count in thousands and millions, so an amount converted here would be the right number in the wrong words for an Indian invoice. The rupee waits for a lakh-and-crore number system of its own.