The Joyo Kanji are the 2,136 characters listed in the Joyo Kanji Table, last revised in 2010. The table is defined as "a guideline for kanji usage when writing modern Japanese in general social contexts such as legislation, official documents, newspapers, magazines, and broadcasting." While not legally binding, newspapers and publishers use it as the primary reference for deciding which kanji to use and which to avoid.

The history of the Joyo Kanji Table dates back to the 1946 Toyo Kanji Table (1,850 characters), which had a restrictive character, strongly discouraging the use of kanji outside the list. In 1981, it was replaced by the Joyo Kanji Table (1,945 characters), which adopted a softer stance as a "guideline" rather than a restriction. The 2010 revision added 196 characters and removed 5, bringing the total to 2,136. Among the additions were characters used in everyday writing that are visually complex and hard to write by hand, such as the kanji for "depression" and the kanji in the word for "vocabulary."

The Joyo Kanji list has a direct impact on character count in Japanese writing. Newspapers make it a rule to write within the Joyo Kanji set, adding furigana (ruby annotations) to non-Joyo kanji or replacing them with hiragana or katakana. Writing a kanji out in kana changes the character count (for example, the two-kanji word for "hesitation" becomes five hiragana characters and the single kanji for "jaw" becomes two), so the scope of the Joyo Kanji list directly affects the length of a text.

In terms of computer character encoding, the JIS X 0208 Level 1 kanji set (2,965 characters) does not include every Joyo Kanji: the characters for "depression" and "vocabulary" added in 2010 belong to Level 2. Four of the glyph forms listed in the table (𠮟, 塡, 剝, 頰) are absent from JIS X 0208 altogether and cannot be represented in Shift_JIS, although the table also permits the forms 叱, 填, 剥, 頬 on information devices, and those fall within Level 1. Unicode covers all of them, but 𠮟 lies outside the BMP (Basic Multilingual Plane), so a UTF-16 based length function counts it as 2 even though it is one character.

For character counting in practice, knowledge of the Joyo Kanji is useful for designing readability metrics. Text with a high proportion of Joyo Kanji is easier for a general audience to read, while text heavy with non-Joyo kanji gives a specialized or difficult impression. Some text analysis tools calculate the Joyo Kanji usage rate to evaluate the difficulty level of a piece of writing.