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[My dictionary](http://jisho.org/search/%E4%B8%80%E6%98%A8%E5%B9%B4) lists
both いっさくねん and おととし as readings of 一昨年. Which of these are commonly used? Is
there any difference between these two readings?
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2016-07-30T13:26:20.410
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2016-07-30T17:10:43.470
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question
word-choice readings multiple-readings
pronunciation of 一昨年
おととし is far more common in everyday conversations with your friends and
colleagues, whereas いっさくねん is used mainly in formal speeches and
presentations. いっさくねん is the on-yomi of this word, so it's not surprising that
いっさくねん sounds more formal and/or technical than おととし.

However, when people write おととし, they tend to use hiragana (it depends on the
writer's taste). This is partly because おととし is a non-straightforward 熟字訓.

> 7.「一昨日」「明後日」「一昨年」は、「おととい」「あさって」「おととし」というように、ふつうひらがなで書きます。(from
> [東京外国語大学言語モジュール](http://www.coelang.tufs.ac.jp/mt/ja/gmod/courses/c02/lesson12/step1/explanation/020.html))

So when you see 一昨年 actually written on paper, and have to read it out loud,
いっさくねん may be a better choice.
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2016-07-30T17:10:43.470
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2016-07-30T17:10:43.470
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answer