WHITE MOUNTAINS INSURANCE GROUP LTD WTM

election_required = True...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 these Shares at or below the Purchase Price 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 300,000 Shares, and the Purchase Price is an amount between $385 and $435 per Sh...

expiry = 2011-09-15...BY WHITE MOUNTAINS INSURANCE GROUP, LTD. OF UP TO 300,000 OF ITS COMMON SHARES AT A PURCHASE PRICE NOT GREATER THAN $435 OR LESS THAN $385 PER SHARE THE OFFER, PRORATION PERIOD AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON SEPTEMBER 15, 2011, 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 August 16, 2011, the last full trading day before the public announcement of the Offer, the last reported closing sale price of the Shares on the NYSE was $403.00 per Share. SHAREHOLDERS ARE URGED TO OBTAIN A CURRENT MARKET QUOTATION FOR THE SHARES. See...

mechanism = DUTCH...Offer is not conditioned on any minimum number of Shares being tendered by shareholders. See "Section 1. Number of Shares; Proration". How Much Are You Offering To Pay And What Is The Form Of Payment? We are conducting this Offer through a procedure called a "modified Dutch auction". This procedure allows you to select the price (in increments of $1.00) within the price range specified by us at which you are willing to sell your Shares. The price range for the Offer is $385 to $435 per Share. See "Section 1. Number of Shares; Proration". i We will select the lowest purchase price that will allow us to buy 300,000 S...

must_tender_all = True...licable law) are tendered at or below the Purchase Price 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 at the Purchase Price from shareholders who properly tender all of their Shares at or below the Purchase Price and who do not properly withdraw them before the Expiration Date; and •Second, after purchasing all the "odd lots" that were properly tendered at or below the Purchase Price, we will purchase Shares at the Purchase Price from all other holders who properly tender Shares at or below the Purchase Price and wh...

must_tender_all = True...properly tendered at or below the Purchase Price and not properly withdrawn, the Company will purchase Shares in the following order of priority: · First, the Company will purchase all “odd lots” of less than 100 Shares at the Purchase Price from shareholders who properly tender all of their Shares at or below the Purchase Price and who do not properly withdraw them before the expiration date; and · Second, after purchasing all the “odd lots” that were properly tendered at or below the Purchase Price, the Company will purchase Shares at the Purchase Price from all other holders who properly tender Shares at or below the Purchase Pr...

must_tender_all = True...properly tendered at or below the Purchase Price and not properly withdrawn, the Company will purchase Shares in the following order of priority: •First, the Company will purchase all "odd lots" of less than 100 Shares at the Purchase Price from shareholders who properly tender all of their Shares at or below the Purchase Price and who do not properly withdraw them before the expiration date; and •Second, after purchasing all the "odd lots" that were properly tendered at or below the Purchase Price, the Company will purchase Shares at the Purchase Price from all other holders who properly tender Shares at or below the Purchase Pri...

price = USD 385.0-435.0...ied Dutch auction". This procedure allows you to select the price (in increments of $1.00) within the price range specified by us at which you are willing to sell your Shares. The price range for the Offer is $385 to $435 per Share. See "Section 1. Number of Shares; Proration". i We will select the lowest purchase price that will allow us to buy 300,000 Shares or, if a lesser number of Shares is properly tendered, all Shares that are pro...

threshold = 100...acquired the number of Shares that we have offered to purchase. Therefore, we may not purchase all of the Shares that you tender even if you tender them at or below the Purchase Price. 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_OFFEREX-99.(A)(1)(A) 2 a2205326zex-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 300,000 OF ITS COMMON SHARES AT A PURCHASE PRICE NOT GREATER THAN $435 OR LESS THAN $385 PER SHARE THE OFFER, PRORATION PERIOD AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON SEPTEMBER 15, 2011, UNLESS THE OFFER IS EXTENDED (SUCH DATE AND TIME, AS THEY...

txn_type = TENDER_OFFER...r value $1.00 per share (the “Shares”), at a purchase price not greater than $435 or less than $385 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 (as it may be amended or supplemented from time to time, the “Offer to Purchase”) and in the related Letter of Transmittal which together, as they may be supplemented from time to time, constitute the “Offer”), including the proration provisions described therein. The Company will select the lowest price per Share (in multiples of $1.00)...

txn_type = TENDER_OFFER...r value $1.00 per share (the "Shares"), at a purchase price not greater than $435 or less than $385 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 (as it may be amended or supplemented from time to time, the "Offer to Purchase") and in the related Letter of Transmittal which together, as they may be supplemented from time to time, constitute the "Offer"), including the proration provisions described therein. The Company will select the lowest price per Share (in multiples of $1.00)...