It will slow down, and then stop. It's hard to say when for sure- just when the yeast run out of fermentables to eat. It depends on so many things- the health of the yeast, the temperature of the fermentation, the amount of yeast pitched, the ingredients used, etc, that it's hard to say for certain. Generally, the bulk of fermentation is finished within 3-5 days, then the yeast finish up before starting to digest their own waste products.
Usually, fermentations in a cool place are slower than in a warm place. Higher OG wort (with more fermentables) can take a bit longer, and a big amount of yeast pitched can be different than a small amount of yeast.