In the dataset, we have some X Coordinates and Y Coordinates. We’ll interpolate the value for given coordinates.

**Method 1 – Using the FORECAST or FORECAST.LINEAR Function to Interpolate Between Two Values in Excel**

**Steps:**

- Make new rows for the value you want to interpolate. We want to interpolate between 8 and 9, so we chose a value of 8.5 and put it in C14.

- Use the following formula in cell
**C15**.

`=FORECAST(C14,C5:C12,B5:B12)`

The **FORECAST **function determines the interpolated value in cell **C15 **via linear regression. It works on the ranges** B5:B12 **(as **known_Xs**) and **C5:C12 **(as **known_Ys**).

- Hit the
**Enter**button.

- You can also use the following function:

`=FORECAST.LINEAR(C14,C5:C12,B5:B12)`

- Hit
**Enter**.

The **FORECAST **function is getting deprecated by FORECAST.LINEAR, so it might not be available for newer Excel versions.

**Method 2 – Combining Excel XLOOKUP and FORECAST Functions to Interpolate Between Two Values**

Suppose we want to interpolate for the x-value 6 in **B9:C10**.

**Steps:**

- Modify the dataset to place the coordinates.

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

`=XLOOKUP(C14, B5:B12,B5:B12,,-1,1)`

The **XLOOKUP **function looks up the value in **C14**, searches for this value in the range** B5:B12, **and returns the value which is adjacently smaller than **6.5** as it cannot find this exact value in that range and we put **-1 **in this regard. We get **x1 **as **5**.

When we need a value adjacently larger than **6.5**, we use ‘**1**’ instead of ‘**-1**’ in the formula.

- Hit
**Enter**to see the result in cell**F7**.

- Use the following formula in cell
**F8**.

`=XLOOKUP(C14, B5:B12,B5:B12,,1,1)`

- Hit the
**Enter**key and you will see a value above 6 in cell**F8**.

- Use the following formula in cell
**F9**.

`=XLOOKUP(C14, B5:B12,C5:C12,,-1,1)`

- Hit
**Enter**.

- Use this formula in cell
**F10**.

`=XLOOKUP(C14, B5:B12,C5:C12,,1,1)`

- Hit
**Enter**and you will see the**Y Coordinate**that corresponds to**X2.**

- Select cell
**C15**and use the formula given below.

`=FORECAST(C14,F9:F10,F7:F8)`

- Press the
**Enter**key to see the interpolated value in cell**C15**.

Note that the value is different since the FORECAST here has only two values to use as the baseline.

**Method 3 – Inserting INDEX-MATCH with the FORECAST Function to Interpolate Between two Values**

We want to interpolate the x-value 6 in **B9:C10**.

**Steps:**

- Modify the dataset to place the coordinates.

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

`=INDEX(B5:B12,MATCH(C14,B5:B12,1))`

The **MATCH **function returns the position of the cell value of **C14 **in the range** B5:B12**. And then the **INDEX **function returns the value of that position in **B5:B12**. Thus, it returned **x1**.** **

A similar formula is used to determine **x2**,** y1, **and **y2**.

- Hit
**Enter**to see the result in cell**F7**.

- Use the following formula in cell
**F8**.

`=INDEX(B5:B12,MATCH(C14,B5:B12,1)+1)`

- Hit the
**Enter**key, and you will see the next value above 6 in cell**F8**.

- Use the following formula in cell
**F9**.

`=INDEX(C5:C12,MATCH(C14,B5:B12,1))`

- Hit
**Enter**. This returns the Y1 value that corresponds to X1.

- Use the following formula in cell
**F10**.

`=INDEX(C5:C12,MATCH(C14,B5:B12,1)+1)`

- Hit
**Enter**.

- Select cell
**C15**and insert the formula given below.

`=FORECAST(C14,F9:F10,F7:F8)`

- Press the
**Enter**key to see the interpolated value in cell**C15**.

**Method 4 – Interpolating Between Two Values by Applying a Mathematical Formula **

The interpolation formula is given below. It uses an equation of a straight line.

**Steps:**

- Use the following formula in cell
**C15**.

`=C7+(C14-B7)*(C8-C7)/(B8-B7)`

We want to find the interpolated value when the **X Coordinate **is 2.75. For this reason, we chose the first available **X Coordinates **smaller or greater than 2.75 and their corresponding **Y Coordinates **in this dataset.

- Hit
**Enter**to see the interpolated value in cell**C15**.

**Read More: **How to Interpolate in Excel Graph

**Method 5 – Interpolating between Two Values by Joining SLOPE and INTERCEPT Functions**

We want to interpolate for **X is **10.

**Steps:**

- Insert a few cells to store the slope.

- Insert the following formula in cell
**E7:**

`=SLOPE(C5:C12,B5:B12)`

The **SLOPE **function returns the slope/gradient of the linear regression line which is made by the points formed by given **X **and **Y **Coordinates.

- Hit
**Enter**.

- Use the following formula in cell
**E9**to find the**Y-intercept**.

`=INTERCEPT(C5:C12,B5:B12)`

The **INTERCEPT **function returns the **Y-intercept **of the linear regression line which is made by the points formed by given **X **and **Y Coordinates**.

- Hit
**Enter**to see the output in cell**E9**.

- Insert this formula in cell
**C15**.

`=E7*C14+E9`

The formula is a basic straight-line formula, **y=mx+c**, where **m** is the slope and **c** is the intercept.

- Hit
**Enter**to see the interpolated value in cell**C15**.

- Technically, you could combine all the functions to remove the need for helper cells.

**Read More: **How to Interpolate Missing Data in Excel

**Method 6 – Using the Excel GROWTH Function for Nonlinear Interpolation**

Our dataset has a non-linear relation between **Y **and **X Coordinates**.

**Steps: **

- We want to interpolate a value between 5 and 8. Let it be 6.5.

- Use the following formula in cell
**C15**.

`=GROWTH(C5:C12,B5:B12,C14)`

The **GROWTH **function returns the interpolated data by predicting the exponential growth of the **X **and **Y Coordinates**.

- Hit
**Enter**and you will see the interpolated value in cell**C15**.

**Download the Practice Workbook**

## Related Articles

- How to Do Interpolation with GROWTH & TREND Functions in Excel
- How to Do Linear Interpolation in Excel
- How to Perform Bilinear Interpolation in Excel
- How to Use Non-Linear Interpolation in Excel
- How to Do VLOOKUP and Interpolate in Excel
- How to Do Linear Interpolation Excel VBA

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