Minus sign

The minus sign (−) is a mathematical symbol written as a horizontal line. It has two main functions: one is to denote subtraction, the operation between two numbers (for example, 7 − 3), and the other is to indicate that a number is negative (for example, −5).

When used as a subtraction operation, the symbol acts as a binary operator: it requires a number before it and a number after it. When used to mark a negative number, it acts as a unary operator applied to the number, effectively replacing the symbol's position.

Use in mathematics

Subtraction can be defined as addition: a − b is equivalent to a + (−b), where −b is the additive inverse of b, meaning b + (−b) = 0. Subtraction is therefore not commutative: 7 − 3 and 3 − 7 do not give the same result. Similarly, when multiple operations are combined, the order of operations determines the outcome.

Related marks

The minus sign should be distinguished from similar horizontal lines in typography: the hyphen used to join words, the en-dash and em-dash used in grammar, and the longer dash used in ranges. Computer character standards define a specific minus sign character, but many everyday texts use the hyphen key from the keyboard instead.

Uses beyond pure mathematics

The symbol is used to indicate values below zero, such as a temperature of −10 degrees, and in falling mathematical values in finance. In science it denotes direction, for example a force opposing motion, or negative electric charge of electrons.