How to Do Polynomial Interpolation in Excel (With Easy Steps)

Looking for ways to do polynomial interpolation in Excel? Then, this is the right place for you. You can interpolate your data in different ways such as linear, polynomial, exponential etc. Here, you will find a step-by-step way to do polynomial interpolation in Excel.

What Is Interpolation?

Interpolation means predicting a value between two specific given data points using the dataset. Data can be linear or nonlinear and according to that the methods for interpolation also change.

Polynomial Interpolation in Excel: Step-by-Step Procedures

Here, we have a dataset containing the values of X and Y, where Y=F(X). Now, we will show you how you can interpolate polynomially the value of Y from the given value of X by drawing a scatter chart in Excel.

Follow the steps given below to do it on your own dataset.

Step-01: Draw Scatter Chart

In the first step, you have to insert a scatter chart to do polynomial interpolation in Excel.

Here are the steps to do that.

Steps:

Firstly, select cell range B5:C10.
Then, go to the Insert tab >> click on Insert Scatter or Bubble Chart >> select Scatter chart.

Now, you will see that a Scatter Plot has been inserted.

After that, click on the “+” sign to open Chart Elements.
Next, turn on the Axis Titles option.

Then, select the titles and type to change the Axis and Chart Titles according to your wish.

Step-02: Add Polynomial Trendline

Next, we will add Trendline in the Scatter plot to find the equation to interpolate data in Excel.

To start with, click on the “+” sign again to open Chart Elements.
After that, click on the sign beside the Trendline option.
Then, click on More Options.

Now, the Format Trendline toolbox will open.
Afterward, select the Polynomial option and insert Order of the polynomial.
Next, turn on the Display Equation on chart option.

Thus, you can add a polynomial trendline with the equation in your chart.

After that, you can drag the position of the equation and make it more visible if you want.

Step-03: Find & Use Equation Found from Trendline

In the last steps, we will use the equation we found from the trendline to do polynomial interpolation of your data in Excel.

Firstly, select cell F5 and insert the following formula that we found from the polynomial trendline.

=0.8696*F4^3-5.1174*F4^2+70.05*F4+8.4586

Then, press Enter and drag right the Fill Handle tool to AutoFill the formula for the rest of the cells.

Thus, you can do polynomial interpolation by drawing a scatter plot in Excel.

How to Perform Exponential Interpolation in Excel

Additionally, here we will show you how to perform exponential interpolation using the GROWTH function in Excel. This function can predict the exponential growth of data.

The GROWTH function uses the following equation to interpolate data.

y=b*e^x

Here, b is the y-intercept of the curve.

Follow the steps given below to use this function to interpolate your data.

Steps:

In the beginning, insert the following formula in cell F5 and press Enter.

=GROWTH($C$5:$C$10,$B$5:$B$10,F4,TRUE)

After that, drag right the Fill Handle tool to AutoFill the formula for the rest of the cells.

Thus, you can do exponential interpolation in Excel.

In the GROWTH function, we inserted cell range C5:C10 as known_ys, cell range B5:B10 as known_xs, Cell F4 as new_xs and TRUE as const.

Practice Section

In the article, you will find an Excel workbook like the image given below to practice on your own.

Things to Remember

In the beginning, you should check the pattern of your data before interpolating your data, if it is linear or nonlinear.
You can use the FORECAST & TREND functions if your data is linear.
However, polynomial Interpolation is used to interpolate nonlinear data.

Download Practice Workbook

You can download the workbook to practice yourself.

Doing Polynomial Interpolation.xlsx

Conclusion

So, in this article, we have shown you a step-by-step way to do polynomial interpolation in Excel. I hope you found this article interesting and helpful. If something seems difficult to understand, please leave a comment. Please let us know if there are any more alternatives that we may have missed.

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