Summary of Significant Accounting Policies (Policies)	6 Months Ended
Jun. 30, 2022
Accounting Policies [Abstract]
Basis of presentation and consolidation	Basis of Presentation and Consolidation The condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the Company’s accounts and those of its wholly owned Australian subsidiary, Kezar Life Sciences Australia Pty Ltd., which is a proprietary company limited by shares. All intercompany balances and transactions have been eliminated upon consolidation. The condensed consolidated balance sheet at December 31, 2021 has been derived from the audited consolidated financial statements at that date but does not include all information and footnotes required by GAAP for complete financial statements. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements included in the Annual Report.
Unaudited Condensed Consolidated Financial Statements	Unaudited Condensed Consolidated Financial Statements The accompanying financial information as of June 30, 2022 is unaudited. The interim condensed consolidated financial statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of the results of operations for the interim periods covered and of our financial condition at the date of the interim balance sheet. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with GAAP for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying condensed consolidated financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto included in our Annual Report.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Significant items subject to such estimates and assumptions include the stock-based compensation, and accrued research and development costs. Management bases its estimates on historical experience and on various other market-specific relevant assumptions that management believes to be reasonable under the circumstances. Actual results may differ from those estimates. The Company anticipates that the ongoing COVID-19 pandemic, recent geopolitical events and supply-chain concerns could have an impact on our clinical development timelines. Estimates and assumptions about future events and their effects cannot be determined with certainty and therefore require the exercise of judgment. As of the date of issuance of these financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update its estimates, assumptions and judgments or revise the carrying value of its assets or liabilities. These estimates may change as new events occur and additional information is obtained and are recognized in the consolidated financial statements as soon as they become known. Actual results could differ from those estimates and any such differences may be material to the Company’s consolidated financial statements.
Significant Risks and Uncertainties	Significant Risks and Uncertainties The Company has implemented business continuity plans designed to address and mitigate the impact of the ongoing COVID-19 pandemic on its business. The extent to which the ongoing COVID-19 pandemic impacts the Company’s business, preclinical and clinical development and regulatory efforts, corporate development objectives and the value of and market for its common stock, will depend on future developments that are highly uncertain and cannot be predicted with confidence at this time, such as the ultimate duration of the pandemic, travel restrictions, quarantines, social distancing, safety measures and business closure requirements in the United States, Europe, China and other countries where we conduct clinical trials and/or manufacture our product candidates. The global economic slowdown, the overall disruption of global healthcare systems and the other risks and uncertainties associated with the pandemic, geopolitical events and global supply chains could have a material adverse effect on the Company’s business, financial condition, results of operations and growth prospects. In addition, the Company is subject to other challenges and risks specific to its business and its ability to execute on its strategy, as well as risks and uncertainties common to companies in the biotechnology industry with development operations, including, without limitation, risks and uncertainties associated with: obtaining regulatory feedback regarding the Company’s product candidates; delays or problems in the supply of its product candidates; loss of single source suppliers or their failure to comply with manufacturing regulations; identifying, acquiring or in-licensing additional technologies or product candidates; clinical development and the inherent uncertainty of clinical success; the challenges of protecting and enhancing its intellectual property rights; and complying with applicable regulatory requirements.
Recent Accounting Pronouncements	Recent Accounting Pronouncements The Company continues to monitor new accounting pronouncements issued by the Financial Accounting Standards Board (“FASB”) and does not believe any accounting pronouncements issued through the date of this report will have a material impact on the Company’s condensed consolidated financial statements. In June 2022, the FASB issued Accounting Standards Update No. 2022-03, Fair value Measurement (Topic 820): Fair value Measurement of Equity Securities Subject to Contractual Sale Restrictions. This standard clarifies that a contractual restriction on the sale of an equity security is not considered part of the unit of account of the equity security and, therefore, is not considered in measuring fair value. This standard will become effective for the Company on January 1, 2024, and should be applied prospectively. Early adoption is permitted. The adoption is not expected to have a material impact on the Company's condensed consolidated financial statements.
Fair Value Measurements	Financial assets and liabilities are recorded at fair value. The carrying amount of certain financial instruments, including cash and cash equivalents, marketable securities, other current assets, accounts payable and accrued liabilities, approximate fair value due to their relatively short maturities. Assets and liabilities recorded at fair value on a recurring basis in the condensed consolidated balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1: Quoted prices in active markets for identical assets or liabilities. Level 2: Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. The Company applies fair value accounting for all financial assets and liabilities and nonfinancial assets and liabilities that are required to be recognized or disclosed at fair value in the financial statements. The Company determines the fair value of Level 1 assets using quoted prices in active markets for identical assets. The Company reviews trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2022

Basis of Presentation and Consolidation

The condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the Company’s accounts and those of its wholly owned Australian subsidiary, Kezar Life Sciences Australia Pty Ltd., which is a proprietary company limited by shares. All intercompany balances and transactions have been eliminated upon consolidation.

The condensed consolidated balance sheet at December 31, 2021 has been derived from the audited consolidated financial statements at that date but does not include all information and footnotes required by GAAP for complete financial statements. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements included in the Annual Report.

Unaudited Condensed Consolidated Financial Statements

The accompanying financial information as of June 30, 2022 is unaudited. The interim condensed consolidated financial statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers

necessary for the fair statement of the results of operations for the interim periods covered and of our financial condition at the date of the interim balance sheet. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with GAAP for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying condensed consolidated financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto included in our Annual Report.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Significant items subject to such estimates and assumptions include the stock-based compensation, and accrued research and development costs. Management bases its estimates on historical experience and on various other market-specific relevant assumptions that management believes to be reasonable under the circumstances. Actual results may differ from those estimates.

The Company anticipates that the ongoing COVID-19 pandemic, recent geopolitical events and supply-chain concerns could have an impact on our clinical development timelines. Estimates and assumptions about future events and their effects cannot be determined with certainty and therefore require the exercise of judgment. As of the date of issuance of these financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update its estimates, assumptions and judgments or revise the carrying value of its assets or liabilities. These estimates may change as new events occur and additional information is obtained and are recognized in the consolidated financial statements as soon as they become known. Actual results could differ from those estimates and any such differences may be material to the Company’s consolidated financial statements.

Significant Risks and Uncertainties

The Company has implemented business continuity plans designed to address and mitigate the impact of the ongoing COVID-19 pandemic on its business. The extent to which the ongoing COVID-19 pandemic impacts the Company’s business, preclinical and clinical development and regulatory efforts, corporate development objectives and the value of and market for its common stock, will depend on future developments that are highly uncertain and cannot be predicted with confidence at this time, such as the ultimate duration of the pandemic, travel restrictions, quarantines, social distancing, safety measures and business closure requirements in the United States, Europe, China and other countries where we conduct clinical trials and/or manufacture our product candidates. The global economic slowdown, the overall disruption of global healthcare systems and the other risks and uncertainties associated with the pandemic, geopolitical events and global supply chains could have a material adverse effect on the Company’s business, financial condition, results of operations and growth prospects.

In addition, the Company is subject to other challenges and risks specific to its business and its ability to execute on its strategy, as well as risks and uncertainties common to companies in the biotechnology industry with development operations, including, without limitation, risks and uncertainties associated with: obtaining regulatory feedback regarding the Company’s product candidates; delays or problems in the supply of its product candidates; loss of single source suppliers or their failure to comply with manufacturing regulations; identifying, acquiring or in-licensing additional technologies or product candidates; clinical development and the inherent uncertainty of clinical success; the challenges of protecting and enhancing its intellectual property rights; and complying with applicable regulatory requirements.

Recent Accounting Pronouncements

The Company continues to monitor new accounting pronouncements issued by the Financial Accounting Standards Board (“FASB”) and does not believe any accounting pronouncements issued through the date of this report will have a material impact on the Company’s condensed consolidated financial statements.

In June 2022, the FASB issued Accounting Standards Update No. 2022-03, Fair value Measurement (Topic 820): Fair value Measurement of Equity Securities Subject to Contractual Sale Restrictions. This standard clarifies that a contractual restriction on the sale of an equity security is not considered part of the unit of account of the equity security and, therefore, is not considered in measuring fair value. This standard will become effective for the Company on January 1, 2024, and should be applied prospectively. Early adoption is permitted. The adoption is not expected to have a material impact on the Company's condensed consolidated financial statements.

Fair Value Measurements

Financial assets and liabilities are recorded at fair value. The carrying amount of certain financial instruments, including cash and cash equivalents, marketable securities, other current assets, accounts payable and accrued liabilities, approximate fair value due to their relatively short maturities. Assets and liabilities recorded at fair value on a recurring basis in the condensed consolidated balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows:

Level 1: Quoted prices in active markets for identical assets or liabilities.

Level 2: Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability.

The Company applies fair value accounting for all financial assets and liabilities and nonfinancial assets and liabilities that are required to be recognized or disclosed at fair value in the financial statements. The Company determines the fair value of Level 1 assets using quoted prices in active markets for identical assets. The Company reviews trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data.