You're reading this because you searched for how to add a linear regression trendline to an Excel scatter chart, or you saw the title and thought, "Are those even English words?!" We've got you covered with both.

If you know what a linear regression trendline is, then move on. Okay, now that the nerds are gone, let's explain linear regression. Linear means in a line. You knew that. Regression, in math, is figuring out how much one thing depends on another thing. We'll call those two things X and Y.

Let's use the example of tracking the value of a single stock on the stock market over time. X is the time in years and Y is the value in dollars.

We know that the value of a stock changes with the passage of time, and many other things. We can’t control those other things, but we can control when to sell the stock, so we control the time variable. But how dependent is the value of a stock on the passage of time?