How long does it take for a coral reef to form?

The major coral reefs on Earth have taken 5,000 to 10,000 years to form.  Different types of coral grow at different rates with the larger corals growing at about 5-25 mm (0.2-1 cm) per year and staghorn and branching corals growing faster, at a rate of about 20 cm (8 inches) per year.  Ultimately, the rate of growth is affected by environmental factors such as water temperature, water salinity, the turbulence of the water, and the availability of food.