Working out your cash inflow involves making a sales forecast for the coming period.  What do you expect to sell, when, how many and at what price?

A spreadsheet is a table where you can enter expected sales for a number of products for each month and automatically calculate the totals for each period.  Cumulative totals for the year can be built in to the spreadsheet design as well as totals by product, period or geographical location. 

Try to make the forecast as realistic as possible by taking into account forward orders already on your books and seasonal trends which affect your industry.  What is the desired effect of additional marketing activities such as advertising campaigns or participation at trade shows?  You can produce different forecasts quickly by manipulating one or two variables each time, to see how this would affect your income.  Be prepared to review and revise the forecast as the year goes on and new information becomes available.