UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of Earliest Event Reported):

August 4, 2015

Health Net, Inc.

(Exact Name of Registrant as Specified in Charter)

Registrant’s telephone number, including area code: (818) 676-6000

Not Applicable

Former Name or Former Address, if Changed Since Last Report

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

On August 4, 2015, Health Net, Inc. (“we”, “us”, “Health Net” or “our”) issued a press release announcing our financial results for the quarter ended June 30, 2015. The press release contains the non-GAAP financial measure “adjusted days claims payable (DCP).” Adjusted DCP for the second quarter of 2015 was 59.1 days, adjusted DCP for the first quarter of 2015 was 66.3 days and adjusted DCP for the second quarter of 2014 was 64.4 days. Adjusted DCP excludes claims reserve and health plan costs related to our capitation and Medicare Advantage-Prescription Drug payables and costs. The most directly comparable GAAP financial measure to this non-GAAP financial measure is second quarter of 2015 DCP of 47.6 days, first quarter of 2015 DCP of 54.8 days and second quarter of 2014 DCP of 49.0 days.

Management believes that adjusted DCP provides useful information to investors because the adjusted DCP calculation excludes from both claims reserve and health plan costs amounts related to health care costs for which no or minimal reserves are maintained. Therefore, management believes that adjusted DCP may present a more accurate reflection of DCP than does GAAP DCP, which includes such amounts. This non-GAAP financial information should be considered in addition to, not as a substitute for, financial information prepared in accordance with GAAP. A reconciliation of the non-GAAP financial measure to the most directly comparable GAAP financial measure is included in the attached press release. As used herein, “GAAP” refers to accounting principles generally accepted in the United States.

The press release is attached hereto as Exhibit 99.1 and hereby incorporated in this Item 2.02 by reference. The information in this Item 2.02 shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing by Health Net, Inc. under the Securities Act of 1933 or the Exchange Act, except as shall be expressly set forth by specific reference in such filing.

Forward Looking Statements

This Current Report on Form 8-K contains certain forward-looking statements with respect to the financial condition, results of operations and business of Centene Corporation (“Centene”), Health Net and the combined businesses of Centene and Health Net and certain plans and objectives of Centene and Health Net with respect thereto, including the expected benefits of the proposed merger. These forward-looking statements can be identified by the fact that they do not relate only to historical or current facts. Forward-looking statements often use words such as “anticipate”, “target”, “expect”, “estimate”, “intend”, “plan”, “goal”, “believe”, “hope”, “aim”, “continue”, “will”, “may”, “would”, “could” or “should” or other words of similar meaning or the negative thereof. There are several factors which could cause actual plans and results to differ materially from those expressed or implied in forward-looking statements. Such factors include, but are not limited to, the expected closing date of the transaction; the possibility that the expected synergies and value creation from the proposed merger will not be realized, or will not be realized within the expected time period; the risk that the businesses will not be integrated successfully; disruption from the merger making it more difficult to maintain business and operational relationships; the risk that unexpected costs will be incurred; changes in economic conditions, political conditions, changes in federal or state laws or regulations,

including the Patient Protection and Affordable Care Act and the Health Care Education Affordability Reconciliation Act and any regulations enacted thereunder, provider and state contract changes, the outcome of pending legal or regulatory proceedings, reduction in provider payments by governmental payors, the expiration of Centene’s or Health Net’s Medicare or Medicaid managed care contracts by federal or state governments and tax matters; the possibility that the merger does not close, including, but not limited to, due to the failure to satisfy the closing conditions, including the receipt of approval of both Centene’s stockholders and Health Net’s stockholders; the risk that financing for the transaction may not be available on favorable terms; and risks and uncertainties discussed in the reports that Centene and Health Net have filed with the Securities and Exchange Commission (the “SEC”). These forward-looking statements reflect Centene’s and Health Net’s current views with respect to future events and are based on numerous assumptions and assessments made by Centene and Health Net in light of their experience and perception of historical trends, current conditions, business strategies, operating environments, future developments and other factors they believe appropriate. By their nature, forward-looking statements involve known and unknown risks and uncertainties because they relate to events and depend on circumstances that will occur in the future. The factors described in the context of such forward-looking statements in this announcement could cause Centene’s and Health Net’s plans with respect to the proposed merger, actual results, performance or achievements, industry results and developments to differ materially from those expressed in or implied by such forward-looking statements. Although it is believed that the expectations reflected in such forward-looking statements are reasonable, no assurance can be given that such expectations will prove to have been correct and persons reading this announcement are therefore cautioned not to place undue reliance on these forward-looking statements which speak only as of the date of this announcement. Neither Centene nor Health Net assumes any obligation to update the information contained in this announcement (whether as a result of new information, future events or otherwise), except as required by applicable law. A further list and description of risks and uncertainties can be found in Centene’s Annual Report on Form 10-K for the fiscal year ended December 31, 2014 and in its reports on Form 10-Q and Form 8-K as well as in Health Net’s Annual Report on Form 10-K for the fiscal year ended December 31, 2014 and in its reports on Form 10-Q and Form 8-K.

Additional Information and Where to Find It

The proposed merger transaction involving Centene and Health Net will be submitted to the respective stockholders of Centene and Health Net for their consideration. In connection with the proposed merger, Centene will prepare a registration statement on Form S-4 that will include a joint proxy statement/prospectus for the stockholders of Centene and Health Net to be filed with the SEC, and each will mail the joint proxy statement/prospectus to their respective stockholders and file other documents regarding the proposed transaction with the SEC. Centene and Health Net urge investors and stockholders to read the joint proxy statement/prospectus when it becomes available, as well as other documents filed with the SEC, because they will contain important information. Investors and security holders will be able to receive the registration statement containing the joint proxy statement/prospectus and other documents free of charge at the SEC’s web site, http://www.sec.gov. These documents can also be obtained (when they are available) free of charge from Centene upon written request to the Investor Relations Department, Centene Plaza 7700 Forsyth Blvd. St. Louis, MO 63105, (314) 725-4477

or from Centene’s website, http://www.centene.com/investors/, or from Health Net upon written request to the Investor Relations Department, Health Net, Inc. 21650 Oxnard Street Woodland Hills, CA 91367, (800) 291-6911, or from Health Net’s website, www.healthnet.com/InvestorRelations.

Participants in Solicitation

Centene, Health Net and their respective directors and executive officers and other members of management and employees may be deemed to be participants in the solicitation of proxies from the respective stockholders of Centene and Health Net in favor of the merger. Information regarding the persons who may, under the rules of the SEC, be deemed participants in the solicitation of the respective stockholders of Centene and Health Net in connection with the proposed merger will be set forth in the joint proxy statement/prospectus when it is filed with the SEC. You can find information about Centene’s executive officers and directors in its definitive proxy statement for its 2015 Annual Meeting of Stockholders, which was filed with the SEC on March 16, 2015. You can find information about Health Net’s executive officers and directors in its definitive proxy statement for its 2015 Annual Meeting of Stockholders, which was filed with the SEC on March 26, 2015. You can obtain free copies of these documents from Centene and Health Net using the contact information above.

No Offer or Solicitation

This communication shall not constitute an offer to sell or the solicitation of an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offer of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended, and otherwise in accordance with applicable law.

The information set forth under Item 2.02 above is incorporated by reference herein.

Exhibit Index

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.