Mattyice and C-Rider are correct, of course. But.... remember that the yeast don't read and they ferment at whatever rate THEY decide, depending on many variables, especially pitch rate and fermentation temperature. One time you might have visible fermentation finished in 4 days, and another time it might take 2 weeks.
So, the only way to know if your fermentation is done is to take a series of SG(Specific Gravity) readings, which should stay stable before you think about packaging.
One little trick at bottling time; Bottle one in a soda bottle. Squeeze out the excess air before capping. When the bottle is hard, the yeast have produced a good amount of CO2, and the rest of the batch should be carbonated as well.