In telecommunications, an area code overlay complex is a telephone numbering plan that assigns multiple area codes to the same geographic numbering plan area (NPA). Area code overlays are implemented in territories of the North American Numbering Plan (NANP) to mitigate exhaustion of central office codes in growth areas. The method has been in use since 1992, and has been the exclusive method of area code relief since 2007.

From the 1947 inception of the North American Numbering Plan in to 1992, the only method of introducing new area codes was the area code split. It divided an existing numbering plan area (NPA) into multiple regions, one of which retained the existing area code. The other parts were each assigned a new NPA code.

The retaining area was usually the historically more established or developed place, and required no numbering changes. It gained numbering capacity by acquiring the central office codes of the other areas, because those were delegated to a new area code in the process. The existing central office codes in the separated areas are maintained in the new numbering plan area and so that the change for existing subscribers is the change of area code. Thus, only area code references, where present for long-distance calling, required updating in directories, letterheads, and business cards. Local seven-digit dialing was unaffected by the area code change.

With the proliferation of electronic switching systems starting in the 1980s, it became possible to implement another method for expanding numbering plan resources, the area code overlay. In an overlay numbering plan, also called overlay complex, an additional area code is assigned to an existing numbering plan area, thereby avoiding the need for existing customers in the reassigned regions to change telephone numbers. The first use of that solution was in New York City in 1992, when area code 917 was overlaid to two numbering plan areas, Manhattan's area code 212, and area code 718 in the outer boroughs.

The North American Numbering Plan Administrator recognizes several types of overlays:

In a distributed overlay, or all-services overlay, the most common type, an entire existing numbering plan area (NPA) gains another area code serving the entire area.

In a single concentrated overlay, only the high-growth portion of an existing area gains a second area code. This was previously implemented in several numbering plan areas, but all of them have since been expanded to the entire NPA.

In a multiple concentrated overlay, the entire existing numbering plan area gains multiple additional area codes, each of which serves a different subsection of the original. This has never been implemented.