How to Fit a Polynomial Curve in Excel (Step-by-Step)

by Tutor Aspire January 17, 2023

You can use the LINEST() function in Excel to fit a polynomial curve with a certain degree.

For example, you can use the following basic syntax to fit a polynomial curve with a degree of 3:

=LINEST(known_ys, known_xs^{1, 2, 3})

The function returns an array of coefficients that describes the polynomial fit.

The following step-by-step example shows how to use this function to fit a polynomial curve in Excel.

First, let’s create some data to work with:

Next, let’s use the LINEST() function to fit a polynomial curve with a degree of 3 to the dataset:

Excel polynomial fit

Once we press ENTER, an array of coefficients will appear:

Using these coefficients, we can construct the following equation to describe the relationship between x and y:

y = .0218x³ – .2239x² – .6084x + 30.0915

We can also use this equation to calculate the expected value of y, based on the value of x.

For example, suppose x = 4. The expected value of y would be:

y = .0218(4)³ – .2239(4)² – .6084(4) + 30.0915 = 25.47