Forecasting is only structured to focus on what the future will look like for a business, while budget-planning centers around what a business thinks their future should look like and how the business should be operating.
Business, simply put, most often start with the planning process. This process produces a plan that is, along with information about the financial and consumer environment surrounding the business, an input into the forecasting process. Despite this aspect of planning, a budget-plan primarily serves as a starting point and guide post to the business on how the business must operate and what realistic goals to aim for.
Forecasting, on the other hand, is primarily, and above all else, concerned solely with how to collect and process information which can affect your business in the immediate future in positive and/or negative ways. Forecasting includes issues like obtaining pertinent, up-to-the-minute facts, checking for flaws or faults in the information and enacting adjustment within your business plan for inflation and other factors that can seriously impact your fiscal health.