In short, for landlines the split position is set by the area code length: 2-4-4 (2-digit area code), 3-3-4 (3-digit), or 4-2-4 (4-digit). Mobile numbers use 3-4-4 and toll-free numbers 4-3-3. All total 10 to 11 digits, and the longer the area code, the shorter the local exchange code, so only the split position moves.
Where do you split a phone number?
Phone number format refers to the rules for writing phone numbers as text. In Japan, the standard notation separates area code, local exchange code, and subscriber number with hyphens, as in 03-1234-5678. This segmentation visually represents the number's structure and improves readability and memorability.
Where the hyphens go is determined by the number type. Landlines use three blocks (area code - local exchange - subscriber number), and the split shifts between 2-4-4, 3-3-4, and 4-2-4 depending on the area code length. Mobile numbers use a 3-4-4 split and toll-free numbers a 4-3-3 split.
| Number type | Split pattern | Example |
|---|---|---|
| Landline (2-digit area code) | 2-4-4 | 03-1234-5678 |
| Landline (3-digit area code) | 3-3-4 | 045-123-4567 |
| Landline (4-digit area code) | 4-2-4 | 0166-12-3456 |
| Mobile phone | 3-4-4 | 090-1234-5678 |
| Toll-free | 4-3-3 | 0120-123-456 |
Landline numbers always total 10 digits including the area code: the longer the area code, the shorter the local exchange code, so only the split position moves.
For international notation, the E.164 format is standard. To express a Japanese number internationally, remove the leading 0 and prepend country code +81 (e.g., 03-1234-5678 becomes +81-3-1234-5678). Variations using spaces instead of hyphens (+81 3 1234 5678) or parentheses around the area code (+81 (3) 1234-5678) are also used internationally. RFC 3966 defines the tel: URI scheme (tel:+81312345678), used for phone links on web pages.
When entering phone numbers on websites or apps, format variations - presence or absence of hyphens, full-width vs. half-width characters, presence or absence of the leading 0 - become an issue. Phone number validation requires flexible design that accepts various input formats. Google's libphonenumber library is the de facto standard tool for normalizing and validating phone number formats across 200+ countries. See Phone Number Structure Guide for the overall numbering system and Japan Country Code Guide for international notation details.
Q. What if you do not know where to split a phone number?
For landlines, you cannot place the hyphens correctly without knowing the area code length, which ranges from 2 to 5 digits by region. The Ministry of Internal Affairs and Communications publishes the official list of area codes. In practice, a normalization library such as Google's libphonenumber can determine the split position automatically.