There is a forecast function built in to Google Spreadsheets that makes this easy to do for simple cases using a linear regression. The docs for forecast are good and clear.

The basic use case is:

FORECAST(x_value_to_forecast,y_axis_set,x_axis_set)

This function combines the steps of calculations the regression coefficients and applying them to the datasets.

There is a forecast function built in to Google Spreadsheets that makes this easy to do for simple cases using a linear regression. The docs for forecast are good and clear.

The basic use case is:

FORECAST(x_value_to_forecast,y_axis_set,x_axis_set)

This function combines the steps of calculating the regression coefficients and applying them to the datasets.