Give these sales forecasting functions in Excel a good baseline and you can get a handle on future sales business. Some Excel forecast functions and their actions appear in the following chart — keep it handy:

Function What It Does
CORREL The worksheet version of the Analysis ToolPak's Correlation tool. The difference is that CORREL recalculates when the input data changes, and the Correlation tool doesn't. Example: =CORREL(A1:A50, B1:B50). Also, CORREL gives you only one correlation, but the Correlation tool can give you a whole matrix of correlations.
LINEST You can use this function instead of the Analysis ToolPak's Regression tool. (The function's name is an abbreviation of linear estimate.) For simple regression, select a range of two columns and five rows. You need to array-enter this function. Type, for example, =LINEST(A1:A50, B1:B50,,TRUE) and then press Ctrl+Shift+Enter.
TREND This function is handy because it gives you forecast values directly, whereas LINEST gives you an equation that you have to use to get the forecast. For example, use =TREND(A1:A50,B1:B50,B51) where you're forecasting a new value on the basis of what's in B51.
FORECAST The FORECAST function is similar to the TREND function. The syntax is a little different. For example, use =FORECAST(B51,A1:A50,B1:B50) where you're forecasting a new value on the basis of the value in B51. Also, FORECAST handles only one predictor, but TREND can handle multiple predictors.