In **Excel**, **interpolation **allows us to get the value between two points on a graph or curve line. It is used to detect or anticipate the future value that lies between two existing data points. In our dataset, we have **Weeks **and **Sales **values. Sales records are for every alternate (Odd) week. We want to find an in-between sales value for **week 8**. Let’s see, **How to Interpolate in Excel Graph**.

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## Download Practice Workbook

## 6 Ways to Interpolate in Excel Graph

We will see six different methods for interpolating **Excel **graphs. We will get familiar with the functions **TREND**, **SLOPE**, **INTERCEPT**, **FORECAST**, **GROWTH **and use the simple mathematical equation for our calculation.

### Method 1: Mathematical Equation for Linear Interpolation

- First of all, we will
**add a chart**from the given dataset then we will use our mathematical function which is :

`y= y1 + (x-x1)⨯(y2-y1)/(x2-x1)`

**Steps:**

- After that, we will add a trendline to our graph and it is apparent that we have got linear growth data.

- Now, we have to select
**x1**,**x2**,**y1**, and**y2**from the given dataset. We will select above and below our**X**value which is**8**. So our**x1**is**x2**is,**y1**is and**y2**is

- Using these values we will interpolate for week
**8**. Type the following formula in cell**F13**

`=F9+(F12-F7)*(F10-F9)/(F8-F7)`

- Now, press the
**ENTER**key.

- So, what we want is, how to show this interpolated value in the graph.
**Right-click**on the graph and click**Select Data**.

- After that, click
**Add**from the popped-up**dialogue box**.

- What we have to do now is, to select the
**X**and**Y**cells.

- Finally, click
**OK**.

That’s it.

**Read More:** **How to Do Linear Interpolation in Excel (7 Handy Methods)**

### Method 2: Interpolate in Excel Graph Using Trendline

The **trendline** is one of the easiest methods for interpolating a linear equation.

**Steps:**

- We will add a trendline and graph from the dataset. In case you don’t remember how to do it, just follow
**Method 1**. - Now, right-click on the trendline and select
**Format Trendline**.

- Now, select
**Display Equation on the Chart**.

- As a result, we will see an equation in the cart.

- Now, type the following formula in
**F7**.

`=9.3631*F6 + 0.7202`

- Finally, press the
**ENTER**key.

- Now, follow
**Method 1**, in case you forgot how to add interpolate data in the graph.

### Method 3: Interpolate in Graph Using SLOPE and INTERCEPT Functions

Now, we will see the use of **SLOPE **and **INTERCEPT **functions.

**Steps:**

We will select the dataset, insert a graph and add a trendline to it as we have done in **Method 1**.

- Now, type the following formula in cell
**F7**.

`=SLOPE(C5:C12,B5:B12)*F6+INTERCEPT(C5:C12,B5:B12)`

- After that, press the
**ENTER**key.

- Our final graph chart will look like the following image after adding interpolate value in the graph.

- Follow
**Method 1**, for adding interpolate values in an**Excel**chart.

### Method 4: Using FORECAST Function

Interpolation is one kind of forecasting as we are predicting or anticipating the value. We don’t exactly know the real value exists. So, **Excel **in-built function **FORECAST **comes quite handy in this regard.

**Steps:**

- First, add a chart and trendline using the sample data. (
**Method 1**, if you cannot recall the process ) - Then, type the following formula in cell
**F7**.

`=FORECAST(F6,C5:C12,B5:B12)`

- Now, press the
**ENTER**key.

- After adding, the value to chart our dataset will look like the following image.

Read More:

### Method 5: Interpolation Using TREND Function

Earlier we knew about the **Trendline** equation. Now, we will see the use of the **TREND **function.

**Steps:**

- First, we will add a chart and trendline as we did in
**Method 1**. - Now, type the following formula in cell
**F7.**

`=TREND(C5:C12,B5:B12,F6,1)`

- After that, press the
**ENTER**key.

Finally, add the interpolation value in the chart as we did earlier in **Method 1**.

### Method 6: Interpolation Using GROWTH Functions

**Excel **has another inbuilt function called growth. **GROWTH **function is more reliable and accurate for the exponential and non-linear dataset. Suppose, our dataset looks like the following.

**Steps:**

Insert Chart and add exponential trendline using. You can get help from **Method 1 **in case you are not familiar with the process.

- Type the following formula in cell
**F7**.

`=GROWTH(C5:C12,B5:B12,F6,2)`

- Now, press the
**ENTER**key.

- Then, add the interpolation value in the chart.

**Read More:** **How to Do Interpolation with GROWTH & TREND Functions in Excel**

## Practice Section

The single most crucial aspect in becoming accustomed to these quick approaches is practice. As a result, we’ve attached a practice workbook where you may practice these methods.

## Conclusion

That’s all for the article. These are 6 different methods of how to interpolate in **Excel **graph Based on your preferences, you may choose the best alternative. Please leave them in the comments area if you have any questions or feedback.