Exhibit 99.1

Alleghany

ALLEGHANY CORPORATION AND SUBSIDIARIES

FINANCIAL SUPPLEMENT

2017 and 2016 Prior Period Results for

Alleghany Capital Corporation

Forward-Looking Statements

Certain statements contained in this Financial Supplement may be deemed to be “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. Forward-looking statements may be identified by the use of words such as “may,” “will,” “expect,” “project,” “estimate,” “anticipate,” “plan,” “believe,” “potential,” “should” or the negative versions of those words or other comparable words. Forward-looking statements do not relate solely to historical or current facts, rather they are based on management’s expectations as well as certain assumptions and estimates made by, and information available to, management at the time. These statements are not guarantees of future performance. These forward-looking statements are based upon Alleghany’s current expectations and are subject to a number of uncertainties and risks that could significantly affect current plans, anticipated actions and Alleghany’s future financial condition and results. Factors that could cause these forward-looking statements to differ, possibly materially, from that currently contemplated include:

Additional risks and uncertainties include general economic and political conditions, including the effects of a prolonged U.S. or global economic downturn or recession; changes in costs; variations in political, economic or other factors; risks relating to conducting operations in a competitive environment; effects of acquisition and disposition activities, inflation rates, or recessionary or expansive trends; changes in interest rates; extended labor disruptions, civil unrest, or other external factors over which we have no control; changes in our plans, strategies, objectives, expectations, or intentions, which may happen at any time at our discretion; and other factors discussed in Alleghany’s most recent Annual Report on Form 10-K and subsequent filings with the Securities and Exchange Commission, or the “SEC.” All forward-looking statements speak only as of the date they are made and are based on information available at that time. Alleghany does not undertake any obligation to update or revise any forward-looking statements to reflect subsequent circumstances or events.

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ALLEGHANY CORPORATION AND SUBSIDIARIES

FINANCIAL SUPPLEMENT TABLE OF CONTENTS

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ALLEGHANY CORPORATION AND SUBSIDIARIES

BASIS OF PRESENTATION

Presentation

All financial information contained herein is unaudited. Certain amounts may not reconcile exactly due to rounding differences. Unless otherwise noted, all data is in millions of U.S. dollars.

Definitions

References in this financial supplement (the “Financial Supplement”) to the “Company,” “Alleghany,” “we,” “us,” and “our” refer to Alleghany Corporation and its consolidated subsidiaries unless the context otherwise requires. In addition, unless the context otherwise requires, references to,

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ALLEGHANY CORPORATION AND SUBSIDIARIES

ALLEGHANY CAPITAL RESULTS - FULL YEAR 2017 AND 2016⁽¹⁾

($ in millions)

ALLEGHANY CAPITAL EQUITY⁽⁴⁾

($ in millions)

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ALLEGHANY CORPORATION AND SUBSIDIARIES

ALLEGHANY CAPITAL RESULTS - THREE AND SIX MONTHS ENDED JUNE 30, 2017⁽¹⁾

($ in millions)

ALLEGHANY CAPITAL EQUITY⁽⁴⁾

($ in millions)

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ALLEGHANY CORPORATION AND SUBSIDIARIES

ALLEGHANY CAPITAL RESULTS - THREE AND NINE MONTHS ENDED SEPTEMBER 30, 2017⁽¹⁾

($ in millions)

ALLEGHANY CAPITAL EQUITY⁽⁴⁾

($ in millions)

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ALLEGHANY CORPORATION AND SUBSIDIARIES

ALLEGHANY CAPITAL RESULTS - THREE MONTHS ENDED DECEMBER 31, 2017⁽¹⁾

($ in millions)

ALLEGHANY CAPITAL EQUITY⁽⁴⁾

($ in millions)

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ALLEGHANY CORPORATION AND SUBSIDIARIES

NON-GAAP FINANCIAL MEASURES

Throughout the Financial Supplement, Alleghany’s results of operations are presented in the way that Alleghany believes will be the most meaningful and useful to investors, analysts, rating agencies and others who use financial information in evaluating Alleghany’s performance. The Financial Supplement includes operating earnings before income taxes, which is a “non-GAAP financial measure” under U.S. Securities and Exchange Commission rules and regulations. Non-GAAP financial measures are not meant to be considered in isolation or as a substitute for measures of operating performance prepared in accordance with accounting principles generally accepted in the United States of America, or “GAAP.”

Operating earnings before income taxes represents noninsurance revenue less all operating expenses, and does not include: (i) amortization of intangible assets; (ii) change in the fair value of equity securities; (iii) net realized capital gains; (iv) other than temporary impairment (“OTTI”) losses; and (vii) income taxes. Because operating earnings before income taxes excludes income taxes, change in the fair value of equity securities, net realized capital gains, OTTI losses and amortization of intangible assets, it provides an indication of economic performance that is not affected by investment activity, levels of effective tax rates or levels of amortization resulting from acquisition accounting. Alleghany uses operating earnings before income taxes as a supplement to earnings before income taxes, the most comparable GAAP financial measure, to evaluate the performance of certain of its noninsurance operating subsidiaries and investments. A reconciliation of operating earnings before income taxes to earnings before income taxes is presented on the preceding pages of the Financial Supplement.

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