Mixed costs are costs that contain a portion of both fixed and variable costs.  Common examples include utilities and even your cell phone!  You may be charged a fixed amount each month for data usage or text messages allowed but when you exceed your limit, you are charged a set amount (variable cost) based on each text message or gigabyte of data you use over your limit.

A mixed cost would look like this in a graph:

Next, we will look at how we can estimate the fixed and variable portions of a mixed cost for accounting analysis.