Introduction
Linear interpolation is a valuable technique in Excel that allows you to estimate unknown values that lie between known data points. This method involves fitting a straight line between two data points and using that line to estimate the value at a given point. Linear interpolation is frequently used in data analysis to fill in missing data, create smooth curves, and make predictions based on existing data points.
Key Takeaways
 Linear interpolation in Excel is a valuable technique for estimating unknown values between known data points.
 It is important in data analysis for filling in missing data, creating smooth curves, and making predictions based on existing data points.
 When using linear interpolation, it is crucial to identify and ensure the data set is ordered and complete.
 Setting up the Excel sheet with known data in separate columns and labeling them appropriately is essential for accurate linear interpolation.
 Checking for accuracy by comparing interpolated values with known data points and using validation techniques is crucial for reliable results in data analysis.
Understanding the data
Before we can perform linear interpolation in Excel, it is crucial to have a clear understanding of the data at hand. This involves identifying the data set for interpolation and ensuring that it is ordered and complete.
A. Identify the data set for interpolationFirst and foremost, it is important to identify the specific data set for which linear interpolation is required. This could be a set of values representing a continuous function, such as temperature measurements over time, stock prices at different points, or any other related data points.
B. Ensure the data set is ordered and completeOnce the data set has been identified, it is essential to ensure that it is ordered in a logical sequence. This could involve arranging the values in ascending or descending order, depending on the context of the data. Additionally, it is crucial to check for any missing or incomplete data points within the set, as linear interpolation relies on a continuous and complete data range to accurately estimate values between known data points.
Setting up the Excel sheet
Before we can begin linear interpolating in Excel, we need to set up our spreadsheet with the necessary data and labels.
A. Enter the known data into separate columns
The first step is to enter the known data into the spreadsheet. This typically involves two columns, with the first column representing the independent variable and the second column representing the dependent variable.
B. Label the columns appropriately
Once the data is entered, it's important to label the columns appropriately to ensure clarity and organization. For example, if the first column represents time and the second column represents temperature, the headers for the columns should be labeled as such.
Using the LINEST function
When it comes to linear interpolation in Excel, the LINEST function is a powerful tool that can help you calculate the values between two known data points. In this tutorial, we will provide an overview of the LINEST function and a stepbystep guide on how to use it for linear interpolation.
A. Overview of the LINEST function in ExcelThe LINEST function in Excel is used to calculate the statistics for a line of best fit through a given set of data points. It returns an array that describes the line, including the slope and yintercept. This function is commonly used in linear regression analysis and can be repurposed for linear interpolation.
B. Stepbystep guide on using the LINEST function for linear interpolationHere's a stepbystep guide on how to use the LINEST function for linear interpolation:
 1. Prepare your data: Before using the LINEST function, make sure you have a set of known data points that you want to interpolate between. For example, if you have xvalues in cells A1:A5 and corresponding yvalues in cells B1:B5, make sure your data is organized accordingly.
 2. Use the LINEST function: In a blank cell, enter the following formula: =LINEST(known_y's, known_x's, TRUE, TRUE). Replace "known_y's" with the range of yvalues and "known_x's" with the range of xvalues. The "TRUE, TRUE" parameters tell Excel to return additional statistics, which can be helpful for validating the interpolation.
 3. Extract the slope and yintercept: The LINEST function will return an array of statistics. The first two values in the array represent the slope and yintercept, which are essential for linear interpolation. You can then use these values to calculate the interpolated yvalues for any given xvalue within the range of your known data.
By following these steps, you can effectively utilize the LINEST function for linear interpolation in Excel, allowing you to estimate values between existing data points with confidence.
Interpolating new data points
When working with data in Excel, you may encounter situations where you need to estimate or predict values that fall between known data points. This process, known as linear interpolation, can be easily performed within Excel using the LINEST function and a simple formula.
A. Utilizing the slope and intercept from the LINEST function
The first step in linear interpolation is to calculate the slope and intercept of the line that represents the relationship between the known data points. This can be achieved using the LINEST function in Excel, which returns the slope and intercept of a line that best fits the data. The syntax for the LINEST function is as follows:
 Known_Y's: The known y values
 Known_X's: The known x values
 Constant: TRUE to include the intercept in the calculation, FALSE to exclude it
 Stats: TRUE to return additional statistics, such as the standard error of the slope and intercept, FALSE to only return the slope and intercept
Once you have used the LINEST function to calculate the slope and intercept, you can use these values to interpolate new data points that fall within the range of your known data.
B. Applying the formula for linear interpolation in Excel
Once you have obtained the slope and intercept from the LINEST function, you can use the following formula to perform linear interpolation in Excel:
New Y = Slope * New X + Intercept
Where:
 New Y: The estimated y value for the new data point
 Slope: The slope obtained from the LINEST function
 New X: The x value of the new data point
 Intercept: The intercept obtained from the LINEST function
By plugging in the values for the slope, intercept, and new x value into the formula, you can easily calculate the estimated y value for the new data point using linear interpolation.
Checking for accuracy
When performing linear interpolation in Excel, it is important to ensure the accuracy of the interpolated values. There are a few methods to check for accuracy, including comparing the interpolated values with known data points and using validation techniques.
A. Comparing the interpolated values with known data points
Plot the interpolated values on a graph
One way to check the accuracy of the interpolated values is to plot them on a graph and compare them with the known data points. This visual representation can help identify any discrepancies between the interpolated values and the actual data.

Calculate the error
Another method is to calculate the error between the interpolated values and the known data points. By subtracting the known data points from the interpolated values, you can determine how close the interpolated values are to the actual data.
B. Using validation techniques to ensure accuracy

Use sensitivity analysis
Performing sensitivity analysis can help validate the accuracy of the interpolated values. By adjusting the input data within a reasonable range and observing the changes in the interpolated values, you can verify the reliability of the interpolation.

Compare results with other interpolation methods
Another validation technique is to compare the results of linear interpolation with other interpolation methods, such as polynomial interpolation or spline interpolation. This can help confirm that the linear interpolation is producing accurate results.
Conclusion
In conclusion, linear interpolation in Excel is a useful tool for estimating values between two known data points. By following the simple process of using the LINEST function and basic mathematical calculations, you can accurately predict unknown values within a data set. However, it's important to remember that accuracy is crucial in data analysis. Always doublecheck your calculations and ensure that your data inputs are correct before making any conclusions based on linear interpolation.
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