WHITE MOUNTAINS INSURANCE GROUP LTD WTM

election_required = True...er Than 100 Shares And I Tender All Of My Shares, Will I Be Subject To Proration? If you own beneficially or of record fewer than 100 Shares in the aggregate, properly tender all of your Shares and do not properly withdraw them before the Expiration Date, and complete the section entitled Odd Lots in the Letter of Transmittal and, if applicable, in the Notice of Guarantee Delivery, we will purchase all of your Shares without subjecting them to the proration procedure. See "Section 1. Number of Shares; Proration". Do You Have The Financial Resources To Make Payment? If we purchase 1,000,000 Shares at $500 per Share, then the aggregate cost to us will be approx...

expiry = 2012-03-22...(A) OFFER TO PURCHASE FOR CASH BY WHITE MOUNTAINS INSURANCE GROUP, LTD. OF UP TO 1,000,000 OF ITS COMMON SHARES AT A PURCHASE PRICE OF $500 PER SHARE THE OFFER, PRORATION PERIOD AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON MARCH 22, 2012, UNLESS THE OFFER IS EXTENDED (SUCH DATE AND TIME, AS THEY MAY BE EXTENDED, THE "EXPIRATION DATE"). White Mountains Insurance Group, Ltd., a company organized under the laws of Bermuda (the "Company", "White Mountains", "we" or "us"), is o...

listed = True...er; Termination; Amendment". This Offer is not conditioned upon the receipt of financing or any minimum number of Shares being tendered. This Offer is, however, subject to certain conditions. See "Section 8. Conditions to the Offer". The Shares are listed and traded on the New York Stock Exchange (the "NYSE") under the symbol "WTM" and the Bermuda Stock Exchange under the symbol "WTM-BH". On February 23, 2012, the last reported closing sale price of the Shares on the NYSE was $496.15 per Share. SHAREHOLDERS ARE URGED TO OBTAIN A CURRENT MARKET QUOTATION FOR THE SHARES. See "Section 7. Price Range of Shares; Dividends". On February 22, 2012,...

mechanism = FIXEDEX-99.(A)(1)(A) 2 a2207557zex-99_a1a.htm EX-99.(A)(1)(A) QuickLinks -- Click here to rapidly navigate through this document Exhibit (a)(1)(A) OFFER TO PURCHASE FOR CASH BY WHITE MOUNTAINS INSURANCE GROUP, LTD. OF UP TO 1,000,000 OF ITS COMMON SHARES AT A PURCHASE PRICE OF $500 PER SHARE THE OFFER, PRORATION PERIOD AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON MARCH 22, 2012, UNLESS THE OFFER IS EXTENDED (SUCH DATE AND TIME, AS THEY MAY BE EXTENDED, THE "EXPIRATION DATE"). White Mountains Insurance Group, Ltd., a company organized under the laws of Bermuda (the "Company", "White Mountains",...

must_tender_all = True...as we may elect to purchase, subject to applicable law) are properly tendered and not properly withdrawn, we will accept Shares for purchase in the following order of priority: •First, we will purchase all "odd lots" of less than 100 Shares from shareholders who properly tender all of their Shares and who do not properly withdraw them before the Expiration Date; and •Second, after purchasing all the "odd lots" that were properly tendered, we will purchase Shares from all other holders who properly tender Shares and who do not properly withdraw them before the Expiration Date, on a pro rata basis, with appropriate adjustments to av...

price = USD 500.0...k here to rapidly navigate through this document Exhibit (a)(1)(A) OFFER TO PURCHASE FOR CASH BY WHITE MOUNTAINS INSURANCE GROUP, LTD. OF UP TO 1,000,000 OF ITS COMMON SHARES AT A PURCHASE PRICE OF $500 PER SHARE THE OFFER, PRORATION PERIOD AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON MARCH 22, 2012, UNLESS THE OFFER IS EXTENDED (SUCH DATE AND TIME, AS THEY MAY BE EXTENDED, THE "EXPIRATION DATE")....

priority = True...h Item 12. The fourth paragraph of “Section 4: Acceptance for Payment and Payment for Shares” is hereby amended and restated in its entirety as follows: For purposes of the Offer, the Company will be deemed to have accepted for payment, and thereby purchased, subject to Odd Lot priority and proration, Shares properly tendered and not properly withdrawn, if and when the Company gives oral or written notice to the Depositary, as agent for the tendering shareholders, of the Company’s acceptance for payment of such Shares pursuant to the Offer. Upon the terms and subject to the conditions of the Offer, payment for Shares ac...

threshold = 100...avoid purchases of fractional Shares, until we have acquired the number of Shares that we have offered to purchase. Therefore, we may not purchase all of the Shares that you tender. 3 Odd Lots. The term "odd lots" means all Shares tendered by any person (an "Odd Lot Holder") who owned beneficially or of record a total of fewer than 100 Shares and so certified in the appropriate place on the Letter of Transmittal and, if applicable, on the Notice of Guaranteed Delivery. To qualify for the odd lot preference, an odd lot holder must tender all Shares owned in accordance with the procedures described in Section 4. Odd lots will be accepted for payment before any proration of the...

txn_type = TENDER_OFFER...such lesser number of Shares as is properly tendered and not properly withdrawn, at a price of $500 per Share, net to the seller in cash, less any applicable withholding taxes and without interest, upon the terms and subject to the conditions set forth in the Offer to Purchase dated February 24, 2012 and in the related Letter of Transmittal. This Amendment is being filed in satisfaction of the reporting requirements of Rule 13e-4(c)(3) promulgated under the Securities Exchange Act of 1934, as amended. Except as otherwise set forth below, the information set forth in the Schedule TO, including all exhibits ther...

txn_type = TENDER_OFFEREX-99.(A)(1)(A) 2 a2207557zex-99_a1a.htm EX-99.(A)(1)(A) QuickLinks -- Click here to rapidly navigate through this document Exhibit (a)(1)(A) OFFER TO PURCHASE FOR CASH BY WHITE MOUNTAINS INSURANCE GROUP, LTD. OF UP TO 1,000,000 OF ITS COMMON SHARES AT A PURCHASE PRICE OF $500 PER SHARE THE OFFER, PRORATION PERIOD AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON MARCH 22, 2012, UNLESS THE OFFER IS EXTENDED (SUCH DATE AND TIME, AS THEY MAY BE EXTENDED, THE "EXPIRATION...