Is there any difference between the two idioms back in the day and back in the days? Most of the free online dictionaries only give the version with day, but I have certainly seen native English speakers use both versions--with day and days.

An example from Cambridge Dictionary:

Back in the day, we had an apartment with a swimming pool.

Is this sentence interchangeable with:

Back in the days, we had an apartment with a swimming pool.


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    wiki dictionary identifies it as "misspelling of 'back in the day'" Commented Mar 31, 2021 at 10:36
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    I can imagine back in the days being used like "Back in the days of horse-drawn buggies..." but that's not exactly the same idiom.
    – stangdon
    Commented Mar 31, 2021 at 11:26
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    @stangdon I may be wrong, but it seems to me I've only been hearing the expression 'back in the day' in fairly recent years. I wonder if it has evolved from people saying 'in the days (when I was young/of horse-drawn transport etc.). Commented Mar 31, 2021 at 12:10
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    Back in the day is of relatively recent ('90's) origin. Commented Mar 31, 2021 at 13:08
  • "Back in the day" wasn't around when I was a kid but it's younger than I assumed. Felinius is right. These days non-native English speakers are hypercorrecting the idiom to the more logical "back in the days" like Anton does a couple of times in this video. I'm pretty sure younger generations of native English speakers have been picking this up from world English in popular media. I've definitely noticed it increasing, but mostly still in people with foreign accents so far. Commented Oct 22, 2021 at 22:36

1 Answer 1


Good question. Fascinating NGram supporting Kate's comment about back in the day being a recent development.

Google Ngram Back in The Day vs Back in the Days

To some extent your sentences are not interchangeable. Your second sentence should read something like -

Back in the days of paying rent, we had an apartment with a swimming pool.

Which is like saying -

Back in the day, when we were renters, we had an apartment with a swimming pool.

Back in the Day, is a slangy way of saying, when I was younger or some time ago. The phrase is usually followed by a anecdote describing what someone experienced or how they behaved in their past.

Back in the day, we had to change TV Channels by turning a tiny knob on the TV.

Back in the days is the more traditional usage of the phrase and its usage is slightly different. It is used to establish a time frame and is intended to be more specific than its slangy counterpart. It is generally followed by some illustrative phrase, often starting with the word 'of', intended to establish a time period.

Back in the days of black and white television, we changed channels by turning a tiny knob.

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    To add to that, other variations like "back in those days" (referring to a specific time frame that's clear from context) or "back in my early days" (when I was young or inexperienced) are also fine, even though the illustrative modifier doesn't strictly follow the phrase. Commented Mar 31, 2021 at 19:25

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