The company, which was acquired by social networking giant Facebook in February this year for USD 19 billion, was founded in 2009 by Ukrainian Jan Koum and American Brian Acton.
"Thanks to all of you, half a billion people around the world are now regular, active WhatsApp users," WhatsApp said in a blog post.
It has grown fastest in countries like Brazil, India, Mexico and Russian in the last few months, WhatsApp said.
"Our users are also sharing more than 700 million photos and 100 million videos every single day," it said.
The firm had around 450 million monthly active users globally and more than 320 million daily active users as of March this year.
A Silicon Valley start-up, WhatsApp has been bullish on the use of technology in India for serving the society.
"Doctors in India are using WhatsApp to instantly send electrocardiogram pictures of patients who've suffered heart attacks, saving valuable time and potentially lives," the firm said in a post in February this year.