Home composting usually finishes in about three to five months when the pile is well maintained, according to the U.S. Environmental Protection Agency. A pile that is left untended may take a year or longer to break down. Timing depends on moisture, oxygen, the mix of carbon-rich browns and nitrogen-rich greens, and how often you turn the material; hot, actively managed piles decompose faster than cold, passive ones. The EPA also notes that after the pile stops heating and food scraps are no longer visible, finished compost should cure for at least four weeks before use.
Source: U.S. EPA, “Composting at Home”
Image: Compost bin (photo by Snowmanradio, CC BY-SA 3.0), via Wikimedia Commons.