For the most part, business start-up costs and organizational costs must be deducted over a 180-month (15 year) period. For example, if your start-up costs were $18,000, and you started your business on August 1, 2009, you would be able to deduct $500 in 2009 for your start-up costs. ($18,000 divided by 180 months = $100 per month. If started in August, the business will be operating for five months in 2009.)