Berlin, Germany-based Clue, maker of a fertility tracking app, raised $680,000 (500,000 euros) in a round led by angel Christophe Maire, with additional funding from Joanne Wilson, New York-based Luminary Labs Ventures, and existing investor Thomas Madsen-Mygdal. Before the most recent round, Clue had five angel investors, and after the most recent investment Clue still has less than $1 million in funding.

The funds will be used to grow Clue's development team and bring the app into new markets. The app just launched in Denmark, founder and CEO Ida Tin's home country, because Tin said they had in depth market insight into the country, Denmark is "a very tech savvy country", and there wasn't much competition. So far 40 percent of Clue's users are from the US, which is their biggest market.

Clue uses an algorithm to calculate and predict a woman's next period. Users can add other information to the app as well, including updates on mood, sexual activity, level of flow and other personal notes. While the app can be used to conceive, the developers specify it should not be used to avoid pregnancy.

"When we started thinking about this and I had the idea, [fertility apps] wasn't even a segment," Tin said. "Over the last few years, we have seen these serious players coming out with mature products and I think that's a great benefit for us. When Max Levchin launched at AllThingsD, he kind of validated that market and created a lot of interest."

While Tin said another fertility app, Ovuline, has positioned its app as a product for women who want to get pregnant, Tin said Clue will be in the quantified self segment.

"It's about tracking and it's about following women across their different life stages," Tin said. "You need to know what's going on in your body no matter what your goals are."

Eventually, Tin plans to add more features such as natural family planning as a method of contraception. Normally when a woman wants to use family planning as contraception, she said, the woman needs to take her temperature and track her mucous very carefully, which Clue is not currently designed to do.

"I think it's a well-known secret that we are also developing hardware," Tin said. "That's part of why we didn't do an app for natural family planning. We are aspiring to become the next generation for family planning and we are focusing our efforts on doing this very high tech piece of hardware to really bring this whole field to the next level."

Clue graduated from Princeton, New Jersey-based accelerator Tigerlabs Health, an accelerator which aims to draw startups that want to work with pharma companies. While Tin said the company first wants to develop the hardware before making any next steps, Clue is interested in working with pharma companies eventually.

"Given that we are digital, there is a data set to what we're doing that I think would be interesting for pharma," Tin said. "There are possible distribution and branding opportunities [too]."