You know what you weigh now. Instructions for manually calculating the duration of a diet are given on page . As you experiment with various calorie deficits, remember that a deficit of 500 calories a day translates to a loss of 52 pounds per year. If you're patient, you can lose all the weight you want to at that rate.
Larger deficits peel the weight off faster but extract a greater price in hunger along the way.
As the diet progresses you'll see the actual calorie shortfall based on the trend and compare it to the plan. Once you're into the diet and begin to observe a consistent calorie shortfall and weekly weight loss, you can revise the forecast based on the actual numbers you're observing, or adjust your meal plan to achieve the intended rate of reduction.