How do I fix a running toilet without a plumber?

Start by removing the tank lid and identifying the problem. Most running toilets are caused by one of three things: a faulty flapper, a float set too high, or a broken fill valve. First check the flapper, the rubber seal at the bottom of the tank. If it looks warped or worn, replace it by unhooking it and taking it to a hardware store to match the size. It costs about $5 and snaps on easily. If the flapper is fine, check the float. If water is rising above the overflow tube, bend the float arm down or adjust the float screw to lower the water level. If neither fixes it, replace the fill valve, which costs about $10 and comes with simple instructions.