Extrapolation is a way to use math to predict data that goes beyond what is already known. This is done through programming. So it’s a way to evaluate and visualize data in Excel. To extrapolate a graph, we use the data we already have to make a graph and then follow the line to guess what kind of results we will get outside of the data range we already have. Here are step-by-step instructions with explanations on how to extrapolate a graph in Excel.

## How to Extrapolate a Graph in Excel 2 Easy Methods

### 1. Use Trendline Feature to Extrapolate a Graph in Excel

A line of best fit also called a trendline, is a straight or curved line on a chart that shows the overall pattern or direction of the data. Using a trendline to extrapolate from a graph in Excel helps you show how data changes over time. It’s a basic feature of Excel that lets us predict data within a reasonable range. We’ll learn how to add a trendline to a chart here. For an example of the **Trendline** feature in **Excel**, let us consider these two tables.

**Linear Data** shows how much oil is needed to fry potatoes in a restaurant, while **Non-Linear** Data shows how much a store sells over the course of a few months.

We will be extrapolating both these **Linear** and **Non-Linear** graphs with Trendline Feature.

#### 1.1 Extrapolate Linear Graph by Trendline Feature

To extrapolate a **Linear** graph in **Excel,** let us assume we want to find out how much oil is needed for **100** kg of potatoes.

To find that out, we should follow the following steps.

**Steps:**

- At first, choose the range of data (
**B4:C12**). - Secondly, go to the ribbon and click on the
**Insert**tab. - Thirdly, click on the
**Scatter**chart in the chart area (you can pick up the**Line**chart too).

- Fourthly, click on the (
**+**) sign beside the chart and open**Chart Elements**. - Finally, enable the
**Trendline feature**to predict the expected data from the graph. If you double-click on the graph’s trend line, you can open the**Format Trendline**panel and make your own changes.

Here, we can see that **100** kg of potatoes will need almost **20** liters of oil. We can make this prediction even more accurate by adding more ranges.

#### 1.2 Extrapolate Non-Linear Graph by Trendline Feature

For extrapolating a graph of **Non-Linear data** in excel, let us assume we want to find out the sales for the **8th** and **9th** months from previous data.

Here we will be following those steps below.

**Steps:**

- At first, use the given data to make a
**Scatter**plot by following the steps above for**Linear Data**. - Then, press on the (
**+**) sign beside the chart and open**Chart Elements**. - After that, by selecting
**Trendline**, we can have a**Linear Trendline**. But by choosing the arrow beside, we can have multiple trendline options like**Exponential**,**Moving Average**,**Logarithmic**, and so on.

- By clicking
**More Options**, we can have more types of trendlines and options to edit the trendline.

Here is an example of an **Exponential Trendline**.

Also, we can see **Moving Average Trendline** in the below image. Here we can see **Moving Average** trendline is closer to our real graph.

### 2. Extrapolate Graph in Worksheets

Excel 2016 and later versions have a tool named **Forecast Sheet** that can be used to extrapolate the entire sheet both graphically and mathematically. This tool turns your data into a table that finds the **Lower** and **Upper** confidence bounds and a corresponding **Linear Trendline** graph. Let us consider the following data set. Here we want to find out how much oil is required to fry **50** **kg** of potatoes.

We will follow these steps to extrapolate a graph with this method.

**Steps:**

- In the beginning, we need to select the entire data range (
**B4:C11**). - Next, go to the
**Data**tab in the ribbon and select the**Forecast Sheet**option.

- Furthermore, a dialog box will appear. In the box, find the
**Forecast End**option and set it to the expected value. For us, the expected value is**50**.

- Lastly, clicking the
**Create**button will create a new sheet with a table that has all the data up to**50**kg, as well as the amount of oil that is forecasted, along with an**Upper**and**Lower Confidence Bound**.

It’ll also create a linear graph with a trendline in it.

## Data Extrapolation with FORECAST Function

If you want to extrapolate your data without making charts and graphs, use the **FORECAST **function in **Excel**. You can extrapolate numbers from a linear trend with the help of the **Forecast** function. You can also use a periodic template or a sheet to figure out what to do. Forecast functions come in different forms. Here are some forecast functions that are often used and the steps to do them:

**1. FORECAST Function**

Extrapolation says that the relationship between values that are already known will also hold for values that are not known. The **FORECAST** function helps you figure out how to extrapolate data that has two sets of numbers that match each other. Here are the steps to follow to use the **FORECAST** function:

**Steps:**

- First, select the empty cell we want to forecast. Then click on the function button in the formula bar.

- Then a dialog box will appear. Search for the
**FORECAST**function and select**FORECAST**from the results and click**OK**.

- Again, a dialog box will appear. In this box, for
**X**, select the cell that corresponding cellâ€™s value we need to find out. In our case, that cell carries**100**.

- For
**known_ys**, select all the cells containing known oil amounts.

- For
**known_xs**, select all the cells containing known potato amounts. Then press**OK**.

- Finally, we will have the forecasted value in the empty cell.

**2. Use FORECAST.LINEAR Function**

**The FORECAST.LINEAR function** is the same as the **FORECAST** function. Each and every step is similar as well. Here is an example of this method.

**3. Apply FORECAST.EST Function**

In some cases, there is a seasonal pattern that needs a certain function to be able to predict the future. Then we have to use **the FORECAST.EST function**. Here is the previous example with **FORECAST.EST** function:

## Extrapolate Data with Excel TREND Function

Excel also has a function called the** TREND **function that can be used to extrapolate data without making graphs. Using linear regression, this statistical function will figure out what the next trend will be based on what we already know.Â Here is the previous example of the **FORECAST** function with the **TREND** function.

Here is the output of using the **TREND** function.

## Use Extrapolation Formula to Extrapolate Data

We will put the **Extrapolation Formula** in the formula bar after selecting the desired cell. The extrapolation formula is:

**Y(x) = b+ (x-a)*(d-b)/(c-a)**

Here is an example of this method:

After we apply this equation to the empty cell, we will get the extrapolated value like the picture below.

## Things to Remember

**TREND**and**FORECAST**functions might look like the same thing, but the difference is that the**FORECAST**function only works as a regular formula that returns one value. On the other hand, the**TREND**function is an array formula to figure out how many**y**values go with how many**x**values.**Forecast Sheet**only works when you have a**constant**difference between known values.- Extrapolation isn’t very reliable because we can’t be sure that the trend of the data will continue beyond the range of our data. Also, there is no way to see if our prediction is right or not. But if our original data is consistent, we can use extrapolation to get a better idea.

**Download Practice Workbook**

You can download the practice workbook here.

## Conclusion

This article shows how to use Excel to produce charts and graphs, predict data, and extrapolate graphs. These technologies let us anticipate data and track its changes using graphs and charts. If you’re still having trouble with any of these steps, let us know in the comments. Our team is ready to answer all of your questions.

## Related Articles

- How to Fill a Series Based on Extrapolation in Excel
- How to Perform Linear Extrapolation in Excel
- How to Extrapolate Trendline in Excel

**<< Go Back to Excel Extrapolation | Excel for StatisticsÂ |Â Learn Excel**