So, these two words both mean 'day', but 日期 seems to give much fewer answers than 日子。One dictionary says that both mean 'day' (e.g. Tuesday). Another dictionary says that they both mean 'date' (e.g. 9th April).
Is there an obvious difference between the two, or are they interchangeable?
Thanks all!
日期 = "date", whereas 日子 = "day". Although in Chinese (as in English) they are sometimes interchangeable.
Ordinarily you'd expect a 日期 to have a numerical form:
今天是什么日期？ 今天是2020年4月15号。
What is the date today? Today is the 15-th April, 2020.
However, a 日子 isn't necessarily numerical:
今天是什么日子？ 今天是我的生日。
What day is it today? Today is my birthday.
We typically think of changing the 日期 ("date") rather than the 日子 ("day").
你好，真不好意思，我要改一下日期，可以吗?
Hello, I'm very sorry, I have to change my dates. Is that all right?
ChinesePod
We also typically think of having a good 日子 ("day"), rather than a good 日期 ("date").
今天是个好日子。
Today is a good day.
日子, however, has an additional meaning which 日期 doesn't have.
And that is, it could also mean "life", "living conditions", "livelihood"
Like:-
找了份新工作，日子好过多了 -- (Having found a new job, my life is much better)
