The percent (per cent) sign% is the symbol used to indicate a percentage, a number or ratio as a fraction of 100. Related signs include the permille (per thousand) sign ‰ and the permyriad (per ten thousand) sign ‱ (also known as a basis point), which indicate that a number is divided by one thousand or ten thousand, respectively. Higher proportions use parts-per notation.
Other languages have other rules for spacing in front of the percent sign:
In Czech and in Slovak, the percent sign is spaced with a non-breaking space if the number is used as a noun. In Czech, no space is inserted if the number is used as an adjective (e.g. “a 50% increase”), whereas Slovak uses a non-breaking space in this case as well.
In Finnish, the percent sign is always spaced, and a case suffix can be attached to it using the colon (e.g. 50 %:n kasvu 'an increase of 50%').
In German, the space is prescribed by the regulatory body in the national standard DIN 5008.
In Turkish and some other Turkic languages, the percent sign precedes rather than follows the number, without an intervening space.
In Persian texts, the percent sign may either precede or follow the number, in either case without a space.
In Arabic, the percent sign follows the number; as Arabic is written from right to left, this means that the percent sign is to the left of the number, usually without a space.
In Hebrew, the percent sign is written to the right of the number, just as in English, without an intervening space. This is because numbers in Hebrew (which otherwise is written from right to left) are written from left to right, as in English.
Usage in text
It is often recommended that the percent sign only be used in tables and other places with space restrictions. In running text, it should be spelled out as percent or per cent (often in newspapers). For example, not "Sales increased by 24% over 2006", but rather "Sales increased by 24 percent over 2006".
Prior to 1425 there is no known evidence of a special symbol being used for percentage. The Italian term per cento, "for a hundred", was used as well as several different abbreviations (e.g. "per 100", "p 100", "p cento", etc.). Examples of this can be seen in the 1339 arithmetic text (author unknown) depicted below. The letter p with its descender crossed by a horizontal or diagonal strike conventionally stood for per, por, par, or pur in Medieval and Renaissance palaeography.
1339 arithmetic text in Rara Arithmetica, p. 437
At some point a scribe of some sort used the abbreviation "pc" with a tiny loop or circle (depicting the ending -o used in Italian ordinals, as in primo, secondo, etc. It is analogous to the English "-th" as in "25th") This appears in some additional pages of a 1425 text which were probably added around 1435. This is shown below (source, Rara Arithmetica p. 440).
1425 arithmetic text in Rara Arithmetica, p. 440
The "pc" with a loop eventually evolved into a horizontal fraction sign by 1650 (see below for an example in a 1684 text) and thereafter lost the "per".
1684 arithmetic text in Rara Arithmetica, p. 441
In 1925 D. E. Smith wrote, "The solidus form () is modern."
In the textual representation of URIs, a % immediately followed by a 2-digit hexadecimal number denotes an octet specifying (part of) a character that might otherwise not be allowed in URIs (see percent-encoding).
In SQL, the percent sign is a wildcard character in "LIKE" expressions, for example SELECT * FROM table WHERE fullname LIKE 'Lisa %' will fetch all records whose names start with "Lisa ".
In many programming languages' string formatting operations (performed by functions such as printf and scanf), the percent sign denotes parts of the template string that will be replaced with arguments. (See printf format string.) In Python and Ruby the percent sign is also used as the string formatting operator.
In the command processorsCOMMAND.COM (DOS) and CMD.EXE (OS/2 and Windows), %1, %2,... stand for the first, second,... parameters of a batch file. %0 stands for the specification of the batch file itself as typed on the command line. The % sign is also used similarly in the FOR command.
%VAR1% represents the value of an environment variable named VAR1. Thus:
sets a new value for PATH, that being the old value preceded by "c:\;".
Because these uses give the percent sign special meaning, the sequence %% (two percent signs) is used to represent a literal percent sign, so that:
In linguistics, the percent sign is prepended to an example string to show that it is judged well-formed by some speakers and ill-formed by others. This may be due to differences in dialect or even individual idiolects. This is similar to the asterisk to mark ill-formed strings, the question mark to mark strings where well-formedness is unclear, and the number sign to mark strings that are syntactically well-formed but semantically nonsensical.