A detailed budget is essential for planning a fundraising event, as it will help you manage your expenses, estimate your revenue, and calculate your return on investment. You want to account for all the possible costs of your event, such as venue, catering, entertainment, marketing, staffing, and contingency. You also want to project your income from various sources, such as ticket sales, sponsorships, donations, auctions, and raffles. Don't underestimate your costs, overestimate your revenue, or neglect to monitor and update your budget regularly.