SwiftKey, a British developer of keyboard replacement apps, has raised $17.5m (£11.2m) in a funding round led by venture capital firm Index Ventures.

The company is planning to expand aggressively in the US and Asia, with its chief executive Jon Reynolds moving to its San Francisco office to lead its business from there.

The Series B funding round follows a $2.4m Series A round in 2011, and just over $1.5m of seed funding raised in 2010.

"In the last 12 months, we've had five-times revenue growth. By the end of the year, we forecast our technology will be on 100m devices, up from 30m at the end of 2012," Reynolds told The Guardian.

"We have revenue growth, so it wasn't a case of needing capital to run the core business. It was a case of wanting to invest in the future and to do more faster."

SwiftKey's financial results for 2011 showed a turnover of just under £655k and a net loss of £1.1m for that year. Its 2012 accounts were only published in abbreviated form, but revealed a profit of £1.7m for its TouchType Mobile subsidiary for that year.

"Investment offers us three things - firstly, the ability to rapidly accelerate our product plans and bring ideas to market quicker," said Reynolds.

"Secondly, the resources to grow globally by hiring the very best staff in the UK, US and Asia and boost our investment in R&D. Lastly, it brings us the expertise of a fantastic team at Index."

SwiftKey's product plans include continued investment in its natural language processing (NLP) and machine learning technology, at a time when NLP is an area of focus for Google, Apple and other mobile giants.

While much of this investment focuses on voice rather than text entry, they share core NLP technology. In 2011, Nuance – best known for its speech recognition software – acquired SwiftKey's rival Swype for $102.5m for example.

"NLP has become an increasingly relevant area, and we're at the heart of that. At the centre of our business is the core prediction technology that powers the SwiftKey app - that's what makes our products different and there's more we can do with it," said Reynolds, hinting at announcements on this score by the end of 2013.

"We've always seen it as being about language rather than text input specifically – that's just the first problem we've tried to fix with our technology and approach. We're looking at further boosting our NLP offering and also looking at new ways to apply it."

SwiftKey is also continuing its efforts to preload its typing app on more devices, following a high-profile deal earlier in 2013 to embed it on Samsung's Galaxy S4 Android smartphone.

The company also works with specialist firms in the US healthcare sector to speed up text-entry for doctors, with a range of other clients whose identities SwiftKey keeps private.

"In the last year we've signed our biggest deals to date, and it's been a brilliant opportunity to integrate our technology into some of the most exciting devices around," says Reynolds.

"It's meant our innovations are in the hands of millions more people. When we started, that's what we wanted to achieve, we wanted to build something that would make communicating simpler and easier for millions of people."

SwiftKey founders Jon Reynolds and Ben Medlock

Thus far, SwiftKey's business has been built on Android devices: it had the best-selling paid app on Android's Google Play store in 2012, for example.

"Android has been a major part of our history. When we first launched the app, Android had a tiny market share. As it's grown, we've grown with it," said Reynolds.

"It remains the only platform we could use to show consumers what our technology could do - none of the alternatives would allow us to replace the keyboard across everything you're using on your phone."

However, Reynolds points out that the core technology behind SwiftKey has "always been platform agnostic", and that the company already has an iOS toolkit for its customers in the healthcare industry.

US rival Syntellia recently raised $3m of funding for its Fleksy app, which started on iOS as a standalone app capable of pasting text into other apps to get around Apple's rules, indicating that iOS isn't out of bounds for this app category.

Earlier this year, Apple chief executive Tim Cook was asked directly about keyboard apps during his appearance at the D11 conference in the US.

"On the area of APIs, I think you'll see us open up more in the future," said Cook, spurring rumours that third-party keyboard apps would be allowed in iOS 7. That proved not to be the case.

"We were interested in what Tim Cook said at D11 - we use and enjoy Apple products as a company, we believe we have great technology that makes life easier and we'd love to bring that technology to Apple users," said Reynolds.

SwiftKey is looking beyond Android smartphones and tablets in other ways though: the challenges of text-entry are relevant to other kinds of devices too, from wearable technology like smart watches to the coming generation of connected cars.

"Earlier this year the analyst Mary Meeker said the future would be 'wearables, drivables, scannables, flyables' and she tends to be right! It's definitely a trend we're interested in," said Reynolds.

The original idea for SwiftKey came when he was working in the civil service, watching colleagues do more typing on mobile phones, and struggling with the smaller keyboards that had been shrunk to fit smaller screen sizes.

"This challenge is even greater when you consider text input in cars or wearables," he said. "Accurate, relevant next-word prediction and autocorrection becomes even more relevant, so we are excited by the potential opportunities presented by these new developing product areas."