Gutters and downspouts can become clogged with leaves and other debris, which cause them to overflow. Regularly clean gutters to remove build-up that results in clogs.
Downspouts may be flowing freely, but there may not be an adequate amount of drainage, resulting in overflowing gutters. Adding downspouts or replacing the current downspouts with a larger size may remedy the problem.
The key to stopping gutters from overflowing is to find the cause of the problem. Water overflow from gutters leaks down the side of your home and can damage the foundation and siding. It also can cause erosion problems. Either cleaning out your gutters or increasing drainage should alleviate the problem. According to State Farm, "the best solution between these two is probably adding another downspout because the second downspout can act as a backup if the other gets blocked".