The calculation is actually pretty simple Ratter - If you genuinely wish to lose weight, you need to eat less, exercise more. There is no getting around it, no magic pill, and you cannot compromise on these fundamental points.
Cut back on grazing, snacking. Cut down on portion sizes. Switch out bread, potatoes, meat and eat more fruit and vegetables. Cut back on alcohol consumption - liquid calories, alcohol :)
I am in the same boat, and am trying to change it. I am following something called the 5:2 plan. which is essentially to pretty much eat as normal ( following the basic rules outlined above) for 5 days of the week, but for 2 non-consecutive days of the week eat next to nothing, more or less fasting. It appears to have had good results, based upon some trials etc.
http://www.telegraph.co.uk/foodanddrink/recipes/9781533/The-52-diet-lets-me-have-my-cake-and-eat-it-too.html