Is 四分の一 a natural way of referring to "a quarter" as in "a three-month duration"?

Question

Is 四分の一 a natural way of referring to "a quarter" as in "a three-month duration" (usually e.g. January-March, April-June, July-September, or October-November) in Japanese?

Japanese Stack Overflow uses 四分の一 on its users page to mean "quarter" in this sense, but that looks kind of strange to me. I know that 四分の一 means "one quarter" as in "one fourth" or "25%", but can it also be used (without any other qualifiers, like 年の四分の一) to mean "a three-month duration"?

Also, while we're here, what is the most natural way of referring to "a quarter" in this sense? I'm aware of 四半期; is that the best option?

Answer 1

I agree that "四分の一" in the current Users page of Japanese SE is weird.

四半期【しはんき】 is a technical term that is exclusively used in financial reports, business plans, tax calculation, etc. Generally speaking, you can't use 四半期 in casual/private situations, and you have to use "1年の4分の1" or "3か月" instead:

私は1年の4分の1をハワイで過ごします。
= 私は1年のうち3か月をハワイで過ごします。
([*] 私は四半期をハワイで過ごします。 -- Weird)

However 四半期 can explicitly mean the year is delimited into four at the beginning of months. Only by using 四半期 can people notice the current 四半期 started on October 1st, and the rep count for this 四半期 will end at the end of 2014. If we used "3か月" instead, people would interpret it as "the last 3 months", which is not the case.

So I think 四半期 is the best word that describes the SE's rule, although it may look a bit stiff.

Answer 2

When I read news articles in Japanese, I always see fiscal/yearly quarters referred to by the second phrase you quoted「四半期」So I believe this is the proper term to use when referring to quarters of the year. Looking at a dictionary for this term will give you that same sense.

When I use my GPS (which is set to Japanese), it says 「四分の一マイル」So this seems to be used to referred to fractions of a whole. I suppose if you were to try to use it referring to a year-- you'd say 「四分の一年」, which I would speculate refers to the raw quantity of three months, and not actually a set fiscal segment Q1, Q2, etc like 「四半期」would. This is just speculation on my part though...