Summary

COMPLEX builds a complex number from separate real and imaginary parts. If your worksheet stores those parts in different cells, this function turns them into one valid complex value such as 3+4i or 50+30j.

This matters because Excel's complex-number functions work with complex values as text in a specific format. COMPLEX gives you a clean way to create that format instead of typing the string by hand every time.

Syntax

=COMPLEX(real_num, i_num, [suffix])

The formula has two required numeric parts and one optional notation choice. real_num supplies the value on the real axis, i_num supplies the coefficient of the imaginary unit, and suffix tells Excel whether to write the result with i or j.

For example, =COMPLEX(3,4) returns 3+4i, while =COMPLEX(3,4,"j") returns 3+4j. The numeric value is the same in both cases. Only the displayed notation changes.

One useful detail is that COMPLEX builds the text format expected by Excel's IM functions. That means the result can be passed directly into formulas such as IMSUM, IMSUB, IMREAL, or IMAGINARY without extra cleanup.

Arguments

• real_num - [required] The real part of the complex number.
• i_num - [required] The imaginary part of the complex number.
• [suffix] - [optional] The imaginary suffix to use. Excel accepts "i" or "j". If omitted, Excel uses "i".

real_num and i_num are usually ordinary numbers or cell references. They do not need to be text. Excel combines them into one valid complex-number result, so a formula like =COMPLEX(B1,B2) works naturally when the two components are stored in separate worksheet cells.

suffix is optional, but it matters for notation consistency. In mathematics, i is the usual symbol for the imaginary unit. In electrical engineering, j is often preferred because i may already represent current. Excel allows either one, but it does not accept other suffixes.

It is also worth noting how zero values affect the result. If i_num is 0, Excel can return a purely real-looking value such as 10. If real_num is 0, the result can be purely imaginary, such as 2i or 2j. The formula is still producing a valid complex-number result in both cases.

COMPLEX vs similar functions

COMPLEX is for creating a complex value, while the IM functions usually calculate with one:

Using COMPLEX

The main use is building a valid complex value from separate inputs. That is helpful when the real and imaginary parts are already stored in different cells and you want to pass the result into another complex-number formula such as IMSUM or IMSUB.

The optional suffix matters when your worksheet needs j instead of i. Excel supports both, but you should stay consistent within the same workflow so your formulas are easier to read and maintain.

COMPLEX can also return results that look simpler than you might expect. If the imaginary part is 0, Excel can return just the real number as a complex value. If the real part is 0, the result can be purely imaginary, like 2i.

Example 1 - Build 3+4i

This is the standard use of COMPLEX: take a real component and an imaginary component from separate inputs and assemble them into one valid complex value. That is especially helpful when later formulas need a proper Excel complex-number string rather than two separate numeric cells.

=COMPLEX(3, 4) // Returns "3+4i"

Example 2 - Build a value with j

The mathematics is the same as the previous example, but the notation changes from i to j. That matters in engineering contexts where j is the preferred symbol for the imaginary unit, especially in impedance and AC circuit work where i might already represent current.

=COMPLEX(50, 30, "j") // Returns "50+30j"

Example 3 - Keep the imaginary part at zero

A complex-number workflow does not stop being useful just because one side is zero. This formula produces a valid complex result from a purely real input, which means the value can still move through the same IM-function pipeline as other complex values without needing separate logic for the zero-reactance case.

=COMPLEX(10, 0) // Returns "10"

Example 4 - Create a pure imaginary value

When the real component is zero, Excel returns a purely imaginary result such as 2i. That is useful when the worksheet needs to represent a value that exists only on the imaginary axis, while still keeping it in the format expected by the rest of the engineering functions.

=COMPLEX(0, 2) // Returns "2i"

Quick recap

• Builds a complex value: COMPLEX combines separate real and imaginary parts.
• Supports i or j: Use the optional suffix when you need a specific notation.
• Returns complex text: The result is ready for other IM functions.
• Works well with cell-based inputs: It is especially useful when the two parts start in different cells.
• Handles zero parts cleanly: The result can be purely real or purely imaginary when one side is zero.