App that helps women chart menstrual cycles has 65 million downloads

Few male mainlanders outside the medical profession know as much about women's menstrual cycles as Chai Ke.

The 28-year-old developed the health app Dayima - Putonghua slang for a woman's period - which has been downloaded 65 million times since it was created last year and has more than 21 million registered users.

Women use it to record their periods and get reminders of whether they are on time and what their chances of getting pregnant are on a particular day. Other basic health indicators, such as body mass index, can be recorded for users to get health and dietary tips.

In fact, the app has collected so much data that its makers feel confident enough to hypothesise that mainland women are going longer between periods than the 28 to 30 days widely established. Some wait well over 30 days between periods.

Chai returned to China to start his own business in 2009, after studying operations management and drama in Canada. He launched eight unsuccessful internet-based health services - including one to help diabetics manage their disease - before Dayima became a hit with clients and investors.

He received an investment of 1.5 million yuan (HK$1.9 million) from investor Xu Xiaoping in July last year, followed by US$5 million from Bertelsmann Asia Investments and US$10 million from Sequoia Capital. Chai has put the funds to work on marketing and branding the app along with more research and development.