Nearly one out of every five advertising dollars spent on digital audio during the first half of this year was allocated to podcasts. That’s according to the Interactive Advertising Bureau (IAB) and PwC, which last week reported audio ad billings in the first six months of the year totaled $935 million. PwC partner David Silverman tells Podcast News Daily that 18% of digital audio revenue came from podcasts—or $168.3 million.

That’s up 50% compared to the first half of 2017, when reported podcasting revenue totaled $112.5 million. Actual dollar figures are certainly even higher however since the IAB/PwC report is based on self-reported advertising revenue from the companies it surveyed and they make up less than 100% of the total podcast advertising market. “Audio wasn’t even a category to measure just a few years ago and now it’s half-year revenue in 2018 is double what it was in 2016,” IAB research director Kristina Sruoginis said last week as the numbers were announced. “Podcasting is proving to be a viable ad model,” she added.

Podcasting’s 50% growth rate is even stronger than the 31% increase IAB reported for digital audio ad revenue overall. Even more impressive is the IAB report, produced by PwC, shows digital audio revenue is growing faster than the internet overall. Total digital revenue increased by 23% during the first six months of the year to a record $49.5 billion. “Audio is still in the early stages. It represents about 2% of total revenue but it’s outpacing the growth of the industry in general,” Silverman said. “We see great promise in the use of audio with the advent of smart speakers. As consumers have shifted to mobile, they’re beginning to shift to voice. And as they shift to voice, mobile will play an increasingly larger role.” That’s critical since IAB says 73% of digital audio revenue so far this year has come via mobile platforms.

Even as the IAB and PwC include only the hard data they have from podcasters when it comes to reporting quarterly revenue, their forecast released earlier this year expects those numbers to capture a little more than three-quarters of overall podcast revenue. IAB/PwC project total podcast industry ad revenue will add up to $402 million in 2018. If that figure proves accurate it would be a 28% increase compared to the estimated $313.9 million spent by marketers on podcasts in 2017. And IAB/PwC forecast that pace to continue into 2019 when podcast industry revenue is predicted to hit $514.5 million. And then hit $659 million in 2020. As for the gap between reported and forecast revenue, podcast experts say the gap in the two numbers reflect a still-young industry, and as podcasting becomes more of an ad-supported business they expect revenue reporting data will become more clear-cut. (Follow THIS LINK to join the Podcast News Daily mailing list.)