Are market data fees prorated?

Yes, if you cancel your subscription mid-month then you will receive market data until the last business day of the month. The monthly billing cycle starts on the first U.S. business day of the month.

If you subscribe and unsubscribe on the same day, you might not be charged if you never had that market data service before and did not make any trades…

Market data and research subscription fees are assessed beginning on the day of subscription and billed within the first three U.S. business days of each subsequent month for as long as the services are active.

Additional Information…

If a client changes their market data status mid-month from Professional to Non-Professional the system will terminate any Professional market data and will look for the matching Non-Professional market data package. If there is an exact match, the system will automatically subscribe to the matching Non-Professional market data package and IBKR will issue a refund for the Professional market data subscription. The refund will be given typically on a one day lag from when the Non-Professional data was subscribed to. If there is no matching market data package, the Professional market data package will still be terminated but there will be no refund issued for that month…

Market data subscriptions are offered and billed on a monthly cycle.  If you terminate a subscription mid-month, there is no provision by the exchanges for a partial refund, however, the quote feed will continue through the end of the month for which it was paid…