Pandora to cap free listening to 40 hours per week

(CNN) — If you spend a lot of time listening to Pandora on your mobile phone, you may soon be forced to cut back, or pay up.

To try to manage growing royalty costs – the music service is introducing a 40 hour per month cap for free mobile listening.

Pandora said the cap will allow it to manage the rising cost of what it pays per track, without too much disruption to listeners.

Royalties have risen more than 25 percent over the last three years and are expected to rise another 16 percent by 2015.

Pandora said the average listener only spends about 20 hours per month using the service.

For those who do reach the 40 hour limit on their phones, there are a few ways to keep the music flowing.

Listeners can pay 99 cents for unlimited listening for the rest of the month.

Or pay $3.99 a month for a subscription to Pandora one, which includes unlimited listening and no advertising.

Desktop listeners are exempt from the cap and can listen unlimited for free.

Pandora had more than 65 million listeners at the end of January, up 38 percent from the year before.

The company says the cap will affect less than 4 percent of active listeners.