ClassPass, a startup that gym rats and investors love, is now a $400 million company

ClassPass is a monthly membership program that lets users pay a flat fee to take fitness classes at different gyms and studios.

It's wildly popular in cities across the country, including New York City, where it was founded. Users seem to love it - and investors keep buzzing about it too.

During ClassPass' Series B round of funding in January, investors gave the company a valuation north of $200 million. Onstage Wednesday at TechCrunch Disrupt, ClassPass Chief Executive Payal Kadakia was asked about whether the $200 million figure was still accurate.

"That was earlier this year, and we've doubled since then," Kadakia told TechCrunch's Darrell Etherington. "You guys can do the math."

The company has raised $54 million in venture capital funding since its launch nearly two years ago, but its valuation alone is just one metric for evaluating the company's growth.

When asked about ClassPass's $60 million revenue run rate - a previously public number that elicited murmurs of surprise from the audience - Kadakia said ClassPass is seeing 20% month-over-month growth, and implied that the $60 million figure may be a little low.

In addition to discussing her company's hockey-stick growth, including ClassPass's expansion to more than 20 cities in three countries, Kadakia also discussed the company that pivoted to become ClassPass.

Before ClassPass existed, Kadakia, a world-class dancer, founded a company called Classtivity, a SaaS solution for gym studios to use for registration. But Classtivity never caught on with studios. Kadakia said onstage that she heard "crickets" when pitching Classtivity.

"Failure is an amazing data point that tells you which direction not to go," Kadakia said onstage Wednesday.

Since pivoting, Kadakia says, ClassPass has paid out $30 million to gyms and studios so far, and in 2015 alone, it will pay out $100 million to its partners. ClassPass has booked 4.5 million gym studio reservations since its June 2013 launch and has 95% retention with its studio partners.