If you enter your information into SP's tracker setup, it will provide a range for you. Here's how that range is calculated: www.sparkpeople.com/resource/calorie_calcu
Your range isn't 1200 to 1800 - that's not one SP provides. It generally has a 300 calorie range, but that's twice that. If you had 1200 for your minimum, the top would be 1550.