It's called Sparkpeople.com
You track your daily food and water intake and count all consumed calories.
The nice thing about it is that as your entering your food throughout the day (I recommend this, of course, over entering it all at the end of the day) you know exactly where you are...if you ate too much for breakfast...if your snack was more like a meal...how many calories you have left to consume for dinner....etc.
This is not something I do all the time....not all day every day by any means, but I will do this for a week or 2 every couple months to keep myself on track. It's easy to get off track and over consume or eat the wrong thing, but this puts me right back on track.
There are other programs like this out there, but this is the one I use. Use any one you like...hopefully the outcome will be the same.