How to Use a Trend-Line Equation to Extrapolate Data

Written by ryan menezes
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How to Use a Trend-Line Equation to Extrapolate Data
Steep trend lines describe closely related variables. (Jupiterimages/Goodshoot/Getty Images)

The equation of a trend line describes the relationship between its variables. This equation specifies the value of y, the graph's dependent variable, in terms of x, the graph's independent variable. Not all the points of the graph fall on the trend line, and new data that the chart covers also may not fall on the line. But the equation does offer an approximate way of extrapolating the values of unknown data.

Skill level:
Moderately Easy


  1. 1

    Identify the trend line's gradient from its equation. The gradient is the coefficient of x. For example, if the equation is "y = 3x + 4," the gradient is three.

  2. 2

    Identify the trend line's y-intercept from its equation. The y-intercept is the equation's constant that's independent of x. For example, in the equation "y = 3x + 4," the y-intercept is four.

  3. 3

    Multiply your new data's independent variable by the trend line's gradient. For example, if you are trying to extrapolate data whose independent variable is 35: "35 X 3 = 105."

  4. 4

    Add the y-intercept to this sum: "105 + 4 = 109." This is a reasonable estimate for the dependent variable when the independent variable is 35.

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