Examine the trend line that is on the graph. One of the methods for determining the y-intercept is through observation. Find the x-axis, or horizontal axis on the graph, and locate the value at which x = 0. Place your pencil over this point. Follow the vertical line above this point with your pencil until the pencil intersects the trend line. Look at the y-axis, or vertical axis, and find the value for which this intersection occurs. This value is the y-intercept.

Compare the general equation of a line to the equation of the trend line. The general formula for a line is:

for which m is the slope, b is the y-intercept, x is any x value and y is any y value. By looking at the equation of the trend line, you can determine the y-intercept. For example, if the equation of the trend line is y=2x+5, the y-intercept is 5. You would receive this same answer if you let x = 0.

Review the point-slope formula. If the trend line does not have an equation, then you will want to create one in order to determine the y-intercept. The point-slope formula is:

where m is the slope, y₁ is the y coordinate and x₁ is the x coordinate.

Find the slope of the line. In order to generate the equation of the line, you need to find the slope. The equation of the slope is:

where x₁ and y₁ are one set of coordinates on the trend line and x₂ and y₂ are another set of coordinates on the trend line. For example, two points on the trend line may be (2,9) and (3,11). Putting these points into the equation, you get:

You should calculate an answer of m = 2.

Find another point on the trend line and put the values of the point and the slope into the point-slope formula. For example, if the point is (1,7) and the slope is m = 2, you get:

Solving for y, you receive the equation

Therefore, the y-intercept of the trend line is 5.