Summary

IMSUB subtracts one complex number from another. You give Excel two complex values in text form, such as "3+4i" and "1+2i", and it returns the difference in the same complex-number format.

This is useful when you need to measure a gap between two complex values instead of adding them together. In practice, that can mean checking voltage drop, comparing a live reading to a reference, or removing one signal component from another.

Syntax

=IMSUB(inumber1, inumber2)

The order matters here. Excel subtracts inumber2 from inumber1. For example, =IMSUB("3+4i","1+2i") returns 2+2i.

This function is best read as first minus second. If you reverse the inputs, you reverse the sign of the result. That is especially important when the subtraction is being used to measure drift, drop, or deviation from a reference.

Arguments

• inumber1 - [required] The complex number you are subtracting from.
• inumber2 - [required] The complex number to subtract.

Both inputs need to be valid Excel complex numbers, either typed directly or created with COMPLEX(). When a formula uses more than one complex value, it is best to keep the same suffix style throughout, so do not mix i and j in the same subtraction.

IMSUB vs similar functions

IMSUB is part of the same group as IMSUM and the other complex-number functions, but it solves a different problem:

Using IMSUB

The main thing to remember is that IMSUB follows normal subtraction order. If you reverse the arguments, you reverse the sign of the result. That matters when you are checking whether a reading is above or below a baseline, because =IMSUB(actual, target) and =IMSUB(target, actual) describe two different directions.

Your inputs also need to be valid complex numbers. Excel expects them in a format like x+yi or x+yj, or you can create them with COMPLEX(). Microsoft also notes that IMSUB returns the difference of two complex numbers in that text format, so it fits naturally with the rest of the IM functions.

One practical detail is that the result does not always look fully complex. If the imaginary part cancels out, Excel can return a real-looking result such as 10. If both parts cancel out, the result can be 0. That does not mean IMSUB stopped working. It just means the subtraction removed the complex part completely.

Example 1 - Subtract two complex numbers

This example shows the basic operation clearly: Excel subtracts the real coefficients and the imaginary coefficients in parallel, then returns the result in complex form. That makes IMSUB the direct complex-number equivalent of ordinary subtraction, but without forcing the worksheet to separate the value into multiple helper cells.

=IMSUB("3+4i", "1+2i") // Returns "2+2i"

Example 2 - Find a voltage drop

In an engineering setting, subtraction often represents a drop from one state to another. Here the formula subtracts the load value from the source value and returns the remaining complex difference. Because both the real and imaginary parts are preserved, the result shows more than a simple scalar drop.

=IMSUB("115+10j", "110+5j") // Returns "5+5j"

Example 3 - Remove an imaginary component

This example is useful because it shows how subtraction can isolate one part of a complex value. Removing 5i from 10+5i leaves a purely real result. In practice, that can represent removing an unwanted reactive or phase component from a mixed signal or model output.

=IMSUB("10+5i", "5i") // Returns "10"

Example 4 - Measure drift from a baseline

This pattern is useful when the important question is not the reading itself, but how far it has moved from a reference state. The subtraction returns only the deviation, which in this case is 0.1. That makes IMSUB a practical tool for baseline comparisons in complex-valued measurements.

=IMSUB("2.1+2i", "2+2i") // Returns "0.1"

Quick recap

• Subtracts complex values: IMSUB returns the difference between two complex numbers.
• Order matters: It always calculates inumber1 - inumber2.
• Returns complex text: The result stays in Excel's complex-number format.
• Sometimes the result looks real: If the imaginary part cancels out, Excel may return something like 10 or 0.1.
• Works well with COMPLEX: Use COMPLEX() when your real and imaginary parts start in separate cells.