E.164 is the standard way to write a phone number so any system reads it the same way: a plus sign, the country code and the national number, with no spaces, dashes or parentheses. If you store phone numbers in a CRM or send them to an API, putting them in E.164 format is the first step. It is a short step: it organizes the data, but says nothing about the line itself.
What the E.164 phone number format is
E.164 is the ITU-T recommendation that defines the international numbering plan. A conforming number contains only digits, at most 15 including the country code, and is written with a leading +. The country code is one to three digits and the rest is the national number, without the leading trunk 0 or dialing prefixes such as 00 or 011, which depend on where you call from.
For example, a Buenos Aires mobile typed as 011 15-2345-6789 becomes +5491123456789. The numbers in this article are fictional and only serve as examples.
Common mistakes when storing phone numbers
- Keeping the trunk 0 used for local dialing: 011 instead of 11 after the country code.
- Keeping the 15 on Argentine mobiles, which is local dialing and does not belong in the international format.
- Forgetting the 9 that Argentina inserts between +54 and the area code on mobiles.
- Storing spaces, dashes or parentheses: they look fine but break comparisons and searches.
- Assuming the country: 11 2345 6789 does not say whether it is Argentine or from somewhere else until you decide how to interpret it.
The third one trips up most Latin American data. For the country-specific detail on Argentina, see our guide to Argentine phone numbers.
The country is defined, not guessed
When someone types a number without a +, it has to be interpreted against a reference country, such as the form’s or your market’s. That interpretation country is your decision and should be stored with the number. Do not infer it from the IP address: a person may be traveling, on another provider’s network, or entering a relative’s phone.
What the format tells you and what it does not
A well-formed E.164 number means the structure is right. It does not mean the line exists, is active, belongs to the person who entered it, or will answer a call. It does not tell you whether it has WhatsApp either: ByeBouncer does not check that and does not promise it. A regex that accepts any string of up to 15 digits also does not tell you whether the prefix belongs to a real range in that country.
How to convert a number to E.164 step by step
- Remove spaces, dashes, parentheses and any letters or text.
- If it starts with the international call prefix (00 or 011, depending on the origin country), replace it with +.
- If there is no country code, add it based on the reference country you defined.
- Drop the trunk 0 that goes with the area code and, on Argentine mobiles, the 15.
- For Argentine mobiles, insert the 9 after +54 and before the area code.
- Check that the result has only digits after the + and does not exceed 15.
A numbering library does these steps better than a homemade regex, because it knows each country’s rules and they change over time. Even so, the result is a normalization: if the input had a plausible typo, you will get a well-formed but wrong E.164 number. That is why you should keep the original too.
What to store in your database
- The original number as the person typed it.
- The normalized E.164 number, which you use to compare and deduplicate.
- The country you used to interpret it and where that country came from.
- The validation result with its reason and the date of the lookup.
That date matters: numbers change carrier through portability and get reassigned, so a carrier or line status obtained months ago may have changed. Deduplicating by E.164 avoids repeated contacts that only differ in how the number was written, but it does not decide which of two records is the right one; that rule belongs to your process.
Where ByeBouncer phone validation fits
ByeBouncer validates the phone number separately from your other data. It normalizes the number to E.164 and compares it against the country’s numbering rules. Depending on the query it also returns the carrier and line type; the mobile network status is an additional, optional query. Each result is a separate data point: your team decides what to do with a landline, an unidentified carrier or an undetermined lookup. There is no overall score and no authenticity decision.
If a number cannot be interpreted, do not discard it without reading the reason: the reference country may be missing or there may be a fixable typo. Keep the original number, the normalized one and the country you used to interpret it.
See how phone validation works →
A practical way to start
Normalize in a single place in your system, always store the E.164 value next to the original, and record the interpretation country. Then decide whether your case needs carrier or line type. You can try it with your own numbers and review each result before integrating.
Create an account and try your own numbers →