A thrifty Sydney mum has shared the incredible money hack that helped her save nearly $1000 that she spent on flights to Hawaii.

In what she called the “Coke bottle trick”, teacher Chantal Llamas, 35, simply filled a 600ml Coke bottle with $2 coins.

She said she started off with $20 worth of $2 coins and was shocked with how little space it managed to fill.

“I teach finance literacy at different high schools to help kids be more aware of the responsibility of money and smart ways to save,” Ms Llamas said.

“I was telling them about different tips that I do to save money and then asked them if they had any tricks. That’s when one student told me about the Coke bottle challenge.

“I didn’t believe just filling a 600ml bottle could give you $1000 or anywhere near that. I told my husband about it, and he said, ‘Well, let’s try it then, how hard could it be?’”

As the Coke bottle began to fill up, Ms Llamas said she and her real estate agent husband Daniel, 32, became “crazy” about obtaining as many $2 coins as they could.

“We became really savvy at getting $2 coins,” she said. “My husband would get a small coffee everyday instead of a large, so he would get change from a $5 note.

“If I got two $1 coins, I’d always ask if they could please swap it for a $2. They must have thought it was strange.

“We got so excited every time we got a $2 coin. The more we filled the bottle, the more excited we got and the more we wanted to top it up.

“It seems easy, but then you realise how small the coins actually are.”

She said the Coke bottle sat in the back of their wardrobe.

After nine months, the couple managed to fill up the entire bottle with $880 in coins.

The checked out airfare sales and managed to bag super-cheap return flights to Hawaii for herself and Daniel for just $900, while their son Zachary, now 2, flew for free.

They spent eight “fantastic” days in Hawaii on their first family holiday.

“It was amazing to see we’d saved almost $900 without even really noticing,” Ms Llamas said.

“I’d recommend this to others for sure. It’s a great thing to try and save for a goal.

“It’s such an easy thing to do. Even if you’re a terrible saver or don’t have a huge income, it’s very doable. You don’t really miss a $2 coin. They’re just thrown into the bottom of a bag or on the floor of your car.

“I hope this might inspire others to give it a go. It might take some longer than others, but when it fills up it will all be worth it.”