NEW YORK-- Private equity firm Apax Partners said Tuesday that it completed a tender offer for the common shares of Bankrate Inc. as part of its plan to acquire the consumer finance Web site operator and take it private in a deal valued at about $570.8 million.

The offer expired at midnight Monday. As of that time, a total of about 5.4 million Bankrate shares were validly tendered at a price of $28.50 per share, representing about 28 percent of the company's outstanding shares.

Combined with shares subject to agreements entered into by certain Bankrate directors and officers, the tendered shares represent about 52 percent of the company's outstanding shares.

Apax also exercised an option to buy about 56 million newly issued shares at $28.50 per share, which will bring its ownership of Bankrate common shares to about 80 percent.

Bankrate plans to acquire the rest of outstanding shares. When the acquisition is completed, all remaining outstanding Bankrate shares not tendered will be acquired at $28.50 per share.

Bankrate said in July that it had agreed to be acquired by Apax.