Why new area codes are needed
Each area code has a finite set of assignable phone number blocks. As demand grows, an NPA can approach exhaustion and require a relief plan to introduce additional numbering resources.
If you’re looking for background on how the numbering plan is structured, see How Area Codes Work.
Area code split
A split divides a geographic area into separate regions. One region keeps the original area code, while the other region(s) receive a new area code.
- People and businesses in the newly-created region may need to change their area code.
- Dialing patterns might change, but 10-digit dialing is not automatically required solely because a split occurred.
Area code overlay
An overlay introduces an additional area code to the same geographic region. Existing phone numbers typically keep their current area code; new phone numbers may be assigned the new overlay code.
- Existing numbers usually do not change.
- 10-digit dialing is commonly required for all local calls, because multiple NPAs now serve the same area.
Overlay examples
These are examples from our dataset where an area code is marked as an overlay of another.
Comparison table
| Feature | Split | Overlay |
|---|---|---|
| Do existing numbers change? | Some do (in the new region) | Typically no |
| Geographic boundaries | Divides the region | Same region, multiple NPAs |
| Dialing impact | May vary by region | Often requires 10-digit dialing |
| Customer disruption | Higher (some numbers change) | Lower (numbers usually stay) |
Impact on consumers
If a split occurs, affected customers may need to update contact information and printed materials. If an overlay occurs, the primary change most people notice is 10-digit dialing for local calls.
Regardless of the approach, official announcements and dialing guidance come from local regulators and service providers.
The data in numbers
Relief planning isn't hypothetical — our canonical database, built from NANPA's official records, tracks every US relief action since 1947:
The pattern is clear: splits dominated relief planning through the 1990s, while overlays have been the default since the 2010s — precisely because they avoid changing existing numbers. The full decade-by-decade breakdown is on Statistics, and the codes facing the most pressure are ranked in Which Area Codes Are Running Out Fastest?.
Current trends
Overlays are often used to minimize disruption, since existing numbers usually do not change. You can see the public inputs we use and how we build this dataset on Data Sources.