It's difficult to mix diets. For example, using fitday calorie guidelines is great - and works - when your profile information is correct and you have a plan to log your food and watch your daily calories.
Using Atkins, you are encouraged to not count calories, but severely limit carbs in the induction phase. You're still counting, by the way, just counting carbs. But if you go to the Atkins website, you will find this:
'The Atkins Nutritional Approach counts grams of carbohydrates instead of calories. In Induction, you are allowed 20 grams of Net Carbs. When you progress to Ongoing Weight Loss (OWL), you gradually add carbohydrates in 5-gram increments as you move toward Pre-Maintenance, and finally, in 10-gram increments as you approach the Lifetime Maintenance phase. On the Atkins Nutritional Approach we don’t make you count calories. However for weight loss purposes we suggest you shoot for a healthy range. For women that range is approximately 1500 to 1800 calories. For men that range is approximately 1800 to 2000 calories per day. Be sure to limit empty calories and follow the acceptable foods list for whichever phase you are currently in.'
This is in the diet FAQ.
Looking at fitday, if you plan to lose weight by watching your limits and incorporating a lot of foods (or not restricting foods to certain groups), then that is going to match the the statement that 1500-1800 calories is the range for women to lose weight. However, fitday will have to take into account your BMI and level of activity, your goals and time frame, etc.
If you plan to stay on the Atkins diet, the website lays out the program. You can go to the FAQs for answers to most questions.