It was the week before my husband and I were due to depart on a trip to Canada, the United States and Mexico.

Key points: Some countries can turn travellers away if they don't have at least six months' validity on their passport

Some countries can turn travellers away if they don't have at least six months' validity on their passport However, Australian passports are valid for travel to and from Australia until their final expiry date

However, Australian passports are valid for travel to and from Australia until their final expiry date Sometimes an airline won't let visitors board with less than six months because it can be liable

I thought we were incredibly prepared. It was my third trip to the US and fifth trip overseas.

I had a valid passport, my bags were mostly packed and my visas to Canada and the USA had been approved for months.

But it turned out I wasn't as organised as I thought, when a friend told me I needed at least six months validity remaining on my passport to travel.

I struggled to find any immediate, consistent information to confirm whether the countries I was travelling to would enforce the rule.

So I scrambled to renew my passport in time for my trip, and thankfully everything worked out in the end.

But, this is what I discovered during the panicked process.

A mixed bag of information

The Australian Passport Office website, under the tab "Using your passport" says, "Australian passports are valid for travel to and from Australia until their expiry date".

However, it also says, "some countries may refuse entry to persons with less than six months' validity on their passports beyond the period of intended stay".

The Australian Passport Office website says passports are valid for travel to and from Australia until their expiry date. ( ABC News: Melanie Vujkovic )

The Smart Traveller website, which is run by the Department of Foreign Affairs and Trade, also states that travellers need six months on their passports, under the "Entry and exit" sub-heading of the relevant country being search for.

Travel agents can also advise travellers of this rule, but if they don't it may be written under the terms and conditions of your travel documents.

If you are booking flights yourself, the airline can ask you to tick a box to confirm your passport has six months' validity remaining, but not all do.

The Australian Passport Office advises you check entry requirements of the countries you plan to visit or transit, with the relevant foreign embassy or consulate.

The problem was, it took several days for me to hear back from authorities.

Eventually I found out I probably would have been fine to travel to all three countries on my previous passport.

Mother forced to leave her child behind

Susan Sullivan wasn't so lucky; she was left with no choice but to leave one of her four children behind when travelling to Thailand.

Zali Boyd had to stay behind with family because her passport only had five months validity left. ( Supplied: Susan Sullivan )

She said her nine-year-old daughter Zali was turned away by an airline staff member, saying the country would not allow her in with her current passport.

"At check-in they told me my daughter didn't have enough validity left on it … she had five months left… and that she wouldn't be able to travel without a new passport," Ms Sullivan said.

She said they weighed up several options, but in the end it was too expensive to re-book everyone onto a new flight.

"We went into a bit of a spin … our first instinct was okay everybody get back in the car we're going home," she said.

"We ended up ringing family and a family member came and picked my daughter up from the airport."

Ms Sullivan said while she was generally aware of the rule, she thought all of her children's passports had the same expiry date, and was surprised to hear Thailand enforced it given how frequently Australians travel there.

"I can certainly understand that it would be an issue if someone was planning to go into a country for a couple of months … but not when you're going for five days," she said.

Susan Sullivan and her three boys had to travel to Thailand without her daughter Zali. ( Supplied: Susan Sullivan )

Why doesn't the Australian Passport Office keep us more informed?

Yaric Robinson had to order a priority passport before his trip to Vanuatu this year, after realising he only had four months remaining.

"You get your passport for 10 years, and I just completely forgot about it … having travelled multiple times during that period, it's not something you just think about," he said.

He said the Australian Passport Office should send out reminders, similar to car registrations, closer to the date of expiry.

"It's not something that ever comes up … particularly because it's a 10-year thing, it's not something you're always going to remember 10 years down the track," he said.

Yaric Robinson (left) had to order a priority passport before his trip to Vanuatu this year. ( Supplied: Yaric Robinson )

"It would help if there was an email that said 'by the way your passport expires in 12 months and you need six months to travel'."

His mother, Cathy Robinson, is a travel agent and says she always tells her clients about the rule, and is often met with surprise.

"I've recently had three cases where the very same thing happened," she said.

"But the surprising thing was, [one of the people] then phoned Emirates and Emirates told him that it wouldn't be a problem because they were returning outside of a month of the passport expiry. I had never heard that.

"And it was no problem. But if the airline says they're not going to carry you, it's because that airline is then liable for a $10,000 fine if they let you travel.

"This is one of the reasons why travel agents have always been told, 'doesn't matter where they're going to you just make sure they have a six month validity from their return date', because then you're covered."

The Department of Foreign Affairs and Trade referred me to the Australian Passport Office website when asked about why the validity rule existed, and did not respond to the question about whether a reminder alert would be beneficial to passport holders.

This is what some countries told me about the validity rule