If your passport has less than 6 months validity, in many cases, you may not even be allowed on the plane despite not violating any regulations.
Why passports need to have at least 6 months validity when applying for a visa?
Most countries require that passports have at least 6 months validity when applying for a visa. Even for countries that do not require a visa, upon entry, you must present a passport with validity longer than 6 months. In fact, even at the domestic airport check-in, if your passport has less validity than this, passengers will not be allowed on the plane.
Many people wonder: 'Why can't I enter a country when my passport is valid for another half a year, even though I'm only going on a week-long vacation?' In reality, this regulation has left some people in tears as they've purchased tickets but weren't allowed on the plane, or have arrived at their destination but weren't allowed entry.

The '6 months validity passport' requirement is widespread worldwide. It is applied in over 50 countries and territories, including many places in Asia such as Myanmar, China, Malaysia, Philippines, Singapore, Thailand, Taiwan, Laos, Indonesia, Cambodia, Brunei... as well as the United States and the Middle East region.
Furthermore, European countries within the Schengen area also adhere to the 3 + 3 rule. This means that travelers entering the Schengen area must have a passport valid for at least 3 months from the date of departure, plus an additional 3 months of maximum stay. Therefore, travelers to Europe must also have a 6-month valid passport.
According to Thepointsguy, the reason provided is that many countries issue entry visas for fairly long periods, ranging from 3 to 6 months. Citizens of other countries can stay in these countries for up to six months maximum. Expired passports pose disadvantages to the security management of the respective countries. Passport holders also encounter difficulties when they have to stay to renew their passports at embassies. The best approach is to choose 'prevention is better than cure.'
Some other countries have more lenient regulations, such as only requiring passports to be valid for 3 months from the date of entry, or having one month validity from the date of departure. Canada and Mexico only require passports to be valid for 3 months.

However, to avoid situations where you have to stay longer than planned, past the passport expiration date, it's best to renew your passport about 9 months in advance of the expiration date. The processing time is about 8 working days, with simple procedures.
Instructions for renewing passports:
The application includes:
- 1 completed X01 form
- 2 recent photos, size 4 cm x 6 cm, facing forward with head uncovered, no tinted glasses, against a white background.
- Previous passport
Procedure:
- Submitting application and receiving results in person
- Application acceptance hours: from Monday to Friday and Saturday mornings weekly (excluding holidays, Tet, and Sundays).
- Result return time: from Monday to Friday weekly (except for Tet, holidays, Saturday, and Sunday).
Submission location:
- Immigration Management Department of the Provincial or Centrally-run City Police Department, where you are permanently or temporarily residing.
Result collection location:
- Immigration Management Department of the Provincial or Centrally-run City Police Department, where you are permanently or temporarily residing.
- Through postal services.
Passport issuance fee: 200,000 VND per booklet.
By Ha Nguyen/Star
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Reference: Mytour Travel Handbook
MytourDecember 3, 2018