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A to Z of Excel Functions: The IMARGUMENT Function

6 July 2020

Welcome back to our regular A to Z of Excel Functions blog. Today we look at the IMARGUMENT function.

The IMARGUMENT function

An imaginary number is a complex number that can be written as a real number multiplied by the imaginary unit (sometimes denoted j) which is defined by its property i2 = −1.  In general, the square of an imaginary number bi is −b2.  For example, 9i is an imaginary number, and its square is −81.  Zero is considered to be both real and imaginary.

An imaginary number bi can be added to a real number a to form a complex number of the form a + bi, where the real numbers a and b are called, respectively, the real part and the imaginary part of the complex number.

The IMARGUMENT function returns the argument (theta), an angle expressed in radians, such that:

The IMARGUMENT function employs the following syntax to operate:


The IMARGUMENT function has the following argument:

  • inumber: this is required and represents the complex number for which you want the argument .

It should be further noted that:

  • you should use COMPLEX to convert real and imaginary coefficients into a complex number
  • IMARGUMENT recognises either the i or j notation
  • if the complex number ends in +i or -i (or j), i.e. there is no coefficient between the operator and the imaginary unit, there must be no space, otherwise IMARGUMENT will return an #NUM! error
  • IMARGUMENT is calculated as:


z = x + yi."

Please see my example below:

We’ll continue our A to Z of Excel Functions soon. Keep checking back – there’s a new blog post every business day.

A full page of the function articles can be found here.