It can be costly to fly from Canberra to other capital cities but experts say that's not always the case.

Lillian, this week's Curious Canberran, noticed the price of flights shortly after she moved to the city in 2014.

"I used to drive between Melbourne and Canberra quite frequently and then I thought I would look at flights one day, to see how expensive they were," she said.

"I was really surprised by how much more they cost then say a flight from Melbourne to Sydney."

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To save money, Lillian continues to drive between the cities.

"I think a lot of people are in that situation where it's just so much cheaper to drive, even though it takes seven hours as opposed to one hour," she said.

Lillian's heard a couple of different theories about what contributes to the cost of Canberra's flights, and she was keen to know if any of them were to blame.

There are a handful of factors, some of them unique to Canberra, that push domestic airfares up.

Before we get to those, here's a quick look at how airfares are calculated.

Do Canberrans pay more to fly?

The airlines I contacted didn't comment on specific routes and they're not obligated to breakdown the costs of airfares either due to commercial in confidence.

"The price of flights we find extremely complex," said Tilly South, a campaigns and policy adviser at CHOICE.

"They change minute to minute, day to day, depending on your destination, what type of plane you might be flying in, what airline you're flying with.

"So it's actually quite a complex issue to figure out when prices are going to be more expensive than others."

Qantas, Virgin Australia and Tigerair fly between Canberra and other capital cities. ( ABC News )

Peter Harbison, the executive chairman of CAPA Centre for Aviation, says the price you pay has more to do with when you book your flight and what time you fly.

He used Qantas as an example, pointing out their range of fares from a "bare bones" Red e-deal, to a flexible economy fare, and two business class fares.

"What happens when you're booking very close to a weekend, the special deals dry up," he said.

"That's the way airlines fill their aircraft, so you automatically get bumped up to the flexible fare."

In a statement Virgin Australia said airfares are driven by a combination of factors such as demand and operating costs. ( ABC News: Mark Moore )

To prove his point, Peter compared the price of two flights scheduled to depart the next day.

On the Canberra to Melbourne route he found an economy fare leaving at 5pm for $700 one-way.

He found a Sydney to Melbourne fare leaving at 8.30am for $700 one-way.

"I think the main problem tends to be with the perception that it should be $100 each way... and that in fact is really the cheapest fare," he said

"When you're measuring against that, sure a $1000 round trip Canberra-Melbourne sounds expensive... but if you're travelling in peak hour or at the last minute that's perfectly normal."

Here's what does push prices up:

1. Shorter flights cost more per kilometre

Dr Webber says Canberra-Sydney is one of the shortest routes in Australia.

Dr Tony Webber, CEO of Airline Intelligence & Research and a former Qantas chief economist, says two routes dominate flights into Canberra.

"Sydney-Canberra and Melbourne-Canberra and they are very very short sectors or distances," he said.

"[With] the really short distances you burn a lot of fuel to get up in the air and you burn a lot of fuel going down as well," he said.

"When you spread those costs over a short distance, the cost per kilometre is much higher."

Airport costs and on-route charges also get added to the ticket price.

2. The passenger mix - more work, less play

Some airlines put on additional flights during Parliamentary sitting weeks. ( ABC News: Giulio Saggin )

"One of the reasons Sydney-Canberra costs a lot is that there are a lot of Government corporate deals done," Peter from CAPA Centre for Aviation said.

"The result of that is the airlines have to charge us more - you and me - because the taxpayers are getting a good deal."

Dr Webber says public servants and corporate travellers dominate certain interstate flights.

"On those routes the real driver is the economy and political activity," he said.

"Whereas Sydney to Gold Coast, and even to some extent Sydney to Melbourne, it's more about 'Can we go on sale to motivate people to go on this trip?'"

3. Popularity of the route

Bigger markets are serviced by a greater number of airlines. ( ABC News: Giulio Saggin )

Tilly South from CHOICE says the price of airfares are "similar to any product you might buy in the market - you'll see that usually competition creates lower prices."

"There's a much bigger range of fares in the Sydney-Melbourne market because you've got all of the Jetstar, all of the Tiger, all of the Virgin and Qantas," Peter said.

"It's the third or fourth biggest route in the world so you're going to get much much more competitive fares."

4. Who's flying to town

Competition is also shaped by the number and type of airlines flying into Canberra.

"When you have a route that's dominated by Virgin or Qantas... you unambiguously get higher average airfares than routes that are dominated by low-cost carriers," Dr Webber said.

By re-entering the market, Tigerair has diversified the mix of airlines servicing the city. ( ABC News: Gregory Nelson )

"And that's simply because the full-service carriers have an all-inclusive price that doesn't unbundle services."

The reintroduction of Tigerair in December 2016, put an end to the airline duopoly.

The low-cost carrier will be adding a Canberra-Brisbane route in September.

That's good news for those travelling for leisure.

"If Tiger or Jetstar is flying into your airport... that can be a cheaper option because often business travellers won't book on these airlines," Tilly South said.

Can higher airfares be avoided?

A greater range of fares are available for passengers booking early. ( ABC News: Sonya Gee )

Consumer advocates, aviation experts and the airlines themselves give the same advice - book early to secure lower fares.

"It's always best to travel out of peak times," Tilly said.

"If you can travel in the middle of the day… that's often a bit cheaper than flying in the morning or evening.

"We do find that booking as soon as you can, will get you the cheapest fare."

That's the approach our questioner Lillian takes but she says it doesn't always guarantee a low airfare.

Despite this, she's managed to find an upside to flying in and out of the city.

"One of the benefits of not having that many flights and having quite expensive Canberra flights is that the airport is always so easy to navigate and to get to," she said.

"If I had to choose, it's a great benefit being able to find parking and picking people up, so I wouldn't be able to give that up!"