In order to accurately calculate Weight Watchers points for a piece of Sam's Bakery birthday cake, access the online points calculator that is included with a Weight Watchers membership plan or use an official Weight Watcher Points Plus Calculator available for purchase in stores, online or through Weight Watchers. The current Points Plus system calculates the number of points assigned to each food based on its fat, carbohydrate, fiber and protein content.
There have been several point system diets offered by Weight Watchers. Each year, the diet is renewed as-is or updated with a new point system, food values and target menus. The most current is the 2015 Points Plus. Many websites such as Calculator Cat offer a free online version to calculate food points, but the sites disclaim themselves as not being official Weight Watchers affiliates and may not be accurate.