How to Interpolate Missing Values in Excel

Interpolating missing values in Excel can be done using various methods such as linear interpolation, using the FORECAST function, or using a trendline. In this tutorial, we will focus on linear interpolation.

Linear Interpolation

Linear interpolation is a method of estimating missing values by calculating the average of the values before and after the missing point. This approach assumes that the change between values is linear. Here's how to interpolate missing values using linear interpolation in Excel:

1. Open your Excel workbook and locate the data with missing values.
2. Identify the cells with missing values and the cells with known values before and after the missing values.
3. In an empty cell, type the following formula:

=(ValueAfter - ValueBefore) / (CellAfter - CellBefore) * (CellMissing - CellBefore) + ValueBefore

Replace ValueBefore, ValueAfter, CellBefore, CellAfter, and CellMissing with the corresponding cell references.

4. Press Enter to calculate the interpolated value.
5. Copy the formula and paste it in the cell with the missing value.

Example

Let's assume we have the following dataset with a missing value in cell B4:

To interpolate the missing value in cell B4 using linear interpolation:

1. In an empty cell (e.g., C1), type the following formula:

=(B5 - B3) / (A5 - A3) * (A4 - A3) + B3

2. Press Enter. The interpolated value (30) will appear in cell C1.
3. Copy the value in C1 and paste it in cell B4 to replace the missing value.

Now, the dataset will look like this:

You have successfully interpolated the missing value using linear interpolation in Excel.