Aussies were slugged with $259 million in excess mobile data charges in the last 12 months, almost double the year before, as they continue to embrace mobile broadband as a replacement for struggling fixed-line connections.

Finder.com.au's 2017 Excess Data Charges Report reveals that 19.6 per cent of Australian adults regularly exceed their monthly mobile data allowance, rising from 13.4 per cent in 2016 and only 5.6 per cent in 2015.

The nation's appetite for mobile broadband continues to grow, with a 44.5 per cent leap in mobile data usage in the last financial year, according to the Australian Bureau of Statistics. Australians chewed through 175,076 terabytes via mobile broadband in the three months ending June 30, equating to an average of 2.2 gigabytes per month across the country's 26.3 million mobile services.

Narrowing these figures to only look at smartphone users, this figure leaps to an average of 5.5 gigabytes per month, according to the Australian Communications and Media Authority.

At the same time Australia's mobile broadband speeds continue to increase, allowing mobile users to chew through their data faster than ever while consuming bandwidth-heavy services such as video on demand.

Australia's three major telcos – Telstra, Optus and Vodafone – continue to upgrade their networks and extend their 4G LTE coverage, as well as selling handsets capable of faster download speeds. They're also selling high-speed mobile hotspots capable of supporting all the internet-enabled devices in an average household, along with home fixed-line broadband modems designed to fall back to the mobile network during a fixed-line outage.

Meanwhile the National Broadband Network rollout has only passed half of Australian premises, with only half of those premises signing up for an NBN service. The rollout isn't scheduled to be completed until 2021.

Conservatively estimating that survey respondents exceeded their data cap by just 1 gigabyte, at the average industry cost of $10 per gigabyte, Finder.com.au estimates that as a whole Australians spent at least $259 million on excess data charges in the last 12 months – coughing up an extra $113 million compared to the year before.

Younger Australians are significantly more likely to exceed their allowance, with 36 per cent of Gen Y mobile users regularly going over their data limits compared to only 21 per cent of Gen Xers and only 7 per cent of Baby Boomers.

Despite the rising numbers of Australians regularly exceeding their monthly mobile data allowance, complaints to the Telecommunications Industry Ombudsman regarding excess data fees have continued to fall in recent years.

The fall in complaints comes as the major telcos respond to pressure from the consumer watchdog to reduce excess data fees and improve alerts to let customers know when they're approaching 50, 85 and 100 per cent of their monthly data limit. Along with falling excess data prices, this has significantly reduced bill shock.

The trend to use fast mobile broadband as a substitute for fixed-line connections is a key factor in rising excess data costs – especially among Australians who value LTE's fast upload speeds compared to ADSL and cable broadband, says Finder.com.au telecommunications expert Alex Kidman.

"Aussies on poor ADSL or oversubscribed cable fixed-line plans struggle with basic connectivity, and the allure of faster 4G connections is a tough one to resist," Kidman says.

"At the same time our love affair with streaming services such as Netflix, Foxtel Now and iView bears also much of the blame, because people don't really think about the heavy data cost of video until the mobile bill comes in."

As excess data charges become less oppressive, he says Australians have become more complacent about ensuring that they're on the best plan for their needs. There are signs that excess data charges may rise, with some telcos now charging $12 or $13 per extra gigabyte.

"When it comes to data limits, always choose more than you think you'll need," Kidman says.

"Aussies are drastically underestimating their data needs and what they don't realise is choosing a higher limit is typically a lot cheaper than paying excess data charges."