How to Interpolate in Excel Graph (6 Methods)

In Excel, interpolation allows us to determine the value between two points on a graph or curve. It helps us anticipate future values that lie between existing data points. Let’s explore six methods for interpolation in an Excel graph.

How to interpolate in excel graph


Method 1: Mathematical Equation for Linear Interpolation

Steps:

  • Start by creating a chart from your dataset (Go to INSERT > Scatter).

How to interpolate in excel graph using formula

  • Add a trendline to the graph (assuming linear growth data).

  • Select the x-values (x1 and x2) and corresponding y-values (y1 and y2) around the desired point (e.g., week 8).

How to interpolate in excel graph using formula

  • Use the following formula in cell F13 to interpolate the value for week 8:
=F9+(F12-F7)*(F10-F9)/(F8-F7)

How to interpolate in excel graph using formula

  • Press ENTER.

How to interpolate in excel graph using formula

  • Right-click on the graph, choose Select Data.

How to interpolate in excel graph using formula

  • Click Add from the popped-up dialogue box.

  • Add the interpolated value. Select the X and Y cells.

  • Click OK.

How to interpolate in excel graph using formula

 


Method 2: Interpolation Using Trendline:

Steps:

  • Add a trendline to the graph (similar to Method 1).
  • Right-click the trendline, select Format Trendline, and enable Display Equation on Chart.

How to interpolate in excel graph using trendline

  • The equation displayed represents the interpolated linear relationship.

How to interpolate in excel graph using trendline

  • Calculate the interpolated value for week 8 using the equation.
  • Type the following formula in F7:
=9.3631*F6 + 0.7202

How to interpolate in excel graph using trendline

  • Press ENTER.

  • Follow Method 1, to add interpolate data in the graph.


Method 3 – Interpolation Using SLOPE and INTERCEPT Functions:

Steps:

  • Insert a graph and add a trendline (as in Method 1).
  • In cell F7, use the following formula:
=SLOPE(C5:C12,B5:B12)*F6+INTERCEPT(C5:C12,B5:B12)

How to interpolate in excel graph using slope and intercept

  • Press ENTER to calculate the interpolated value.

  • Herewith the final graph chart, after adding the interpolate value.

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

Method 4: Using FORECAST Function

Steps:

  • Create a chart and add a trendline (similar to Method 1).
  • In cell F7, use the following formula:
=FORECAST(F6,C5:C12,B5:B12)

  • Press ENTER to obtain the interpolated value.

How to interpolate in excel graph by FORECAST function

  • Herewith the final graph chart, after adding the interpolate value.


Method 5: Interpolation Using TREND Function

Steps:

  • Add a chart and trendline as in Method 1.
  • In cell F7, use the following formula:
=TREND(C5:C12,B5:B12,F6,1)

How to interpolate in excel graph by TREND Function

  • Press ENTER to calculate the interpolated value.

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


Method 6: Interpolation Using GROWTH Functions

How to interpolate in excel graph using GROWTH

Steps:

  • Insert a chart and add an exponential trendline (similar to Method 1).
  • In cell F7, use the following formula:
=GROWTH(C5:C12,B5:B12,F6,2)

How to interpolate in excel graph FOR non linear data

  • Press ENTER to find the interpolated value.

  • Add the interpolation value in the chart.

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


Practice Section

We’ve attached a practice workbook so that you can practice these methods.

How to interpolate in excel graph


Download Practice Workbook

You can download the practice workbook from here:


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Mahbubur Rahman
Mahbubur Rahman

MAHBUBUR RAHMAN is a leather engineer with a talent for Excel and a passion for VBA programming. To him, programming is like a time-saving wizard, making data manipulation, file handling, and internet interactions a breeze. His skill set extends to SPSS, STATA, Deep Neural Networks, and Machine Learning. Holding a B.Sc in Leather Engineering from Khulna University of Engineering & Technology, he's shifted to become a content developer. In this role, he crafts technical content centred around Excel... Read Full Bio

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