The importance of tracking becomes really apparent here.  You need to see the breakdown of your meals and know the number of red, amber and green meals.  Take a look at the example below.  Click the image to enlarge it.

In the example, we can see 18 green meals, 2 amber and 5 red, including snacks and days with alcohol (1). Its time to get weighed and see how this formula translates on the scales.

If this formula doesn't get you closer to your goal, you will need to alter it for next week, with fewer red and amber meals and more green ones.

Repeat this every week, you will soon know your magic formula.