NEW YORK, Feb 7 (Reuters) - Bond insurer MBIA Inc (MBI.N: Quote, Profile, Research) has sold $1 billion of its shares at $12.15 each, syndicate sources said Thursday, in an offering that provides much needed capital as it struggles to maintain its credit ratings.

The 82.3 million shares were sold below the stock's closing price of $14.20, down 8 cents on the New York Stock Exchange.

MBIA is boosting capital after writing down positions linked to subprime mortgages and other risky debt. (Reporting by Dan Wilchins; editing by Jeffrey Benkoe)