The phrase "fat chance" can be used as a way of sarcastically describing the impossibility of something, but where did it originate from? I've googled it several times, and it always comes up with the definition, not the origin.

  • 2
    My guess would be that it's either sarcasm, implying it has an extremely slim chance of happening. Or it's implying that it would take an extremely large chance happening to occur. I hope you get a good answer.
    – Wayne
    Commented May 18, 2011 at 1:30
  • See also fat lot of good: english.stackexchange.com/a/47296/9001
    – Hugo
    Commented Oct 27, 2012 at 10:13
  • Could it be to do with the scarcity of food in wartime and the chances of getting fat were rare
    – user135252
    Commented Aug 25, 2015 at 7:01
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    If an expression consisting of normal words is used ironically, i.e. meaning the contrary of the expression you won't find such formulas of irony in etymological dictionaries and questions about the origin of an ironic formula won't get you far.
    – rogermue
    Commented Aug 25, 2015 at 8:51

2 Answers 2


I believe this simply derives from one sense of the word fat:

fat 2a well filled out : of sizable proportions : THICK <a ~ letter> <a ~ volume of verse> : BIG <a resistor spark plug ... permits a wider gap, thus a fatter hotter spark — Newsweek> : unusually large <he had to pay a ~ price to move his factory — Martin Turnell> [Websters 3rd New Int'l Dictionary]

The term is used ironically. At face value it means there is a large chance of something happening, but underneath it really means there is a slim chance after all.

  • BTW, there are a few similar examples of phrases that can be used ironically, such as "smart move" and "big deal"
    – Vitali
    Commented Apr 17, 2020 at 11:45

My English as second language wife jokingly asked about it the other day. My hypothesis (no research to validate) was that it could originate from probability theory. The chances (odds) of something happening are representing in statistics as a distribution. People are familiar with the shape of a normal distribution. https://en.wikipedia.org/wiki/Normal_distribution.

The more narrow the shape, provides a more narrow range and higher probability within this range of an occurrence. The fatter the shape distributes the odds of something happening across a much wider range with less chance for each # represented. Hence, a fat (wider) distribution represents a lower chance hence 'fat chance'


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