Is the expression 'half a percent' acceptable in formal English?

When central banks raise or lower interest rates the radio announcer will say for example:

an increase of one half of one percent

Informally people use half a percent instead, which is less wordy, but is it also incorrect? Ngrams analysis shows publishers favour the longer version, although the short form seems to be gaining some traction.

Thinking about it, I'd never offer someone one half of one pizza; that sounds weird. However, I believe of is necessary here, in combination with an article, quantifier or pronoun. Is this correct?

Solution 1:

In short: yes, “half a percent” is accepted usage, even in formal writing.

To back it up: the New Oxford American English lists percent as both an adverb (“a 1.8 percent increase”) and a noun (“a reduction of half a percent or so in price”). Note that the second example nicely answers your question.

Solution 2:

The phrase half a(n) X is a well-established English idiom. The use of percent here is a straightforward application of the idiom:

• half a cup of water
• half a loaf of bread
• half a dozen
• half a percent

In financial contexts, the more formal version may be preferred, but there's nothing wrong with the informal equivalent.

Solution 3:

Yes.

People in the financial world will sometimes say 50 basis points (itself often shortened to 50 bips in speech). A basis point is one percent of one percent.

But in colloquial, mainstream English, half a percent is perfectly fine.

PW