Summary of Significant Accounting Policies	3 Months Ended
Mar. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Note 2. Summary of significant accounting policies Basis of presentation and consolidation The accompanying interim unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States, or U.S. GAAP, and applicable rules and regulations of the Securities and Exchange Commission, or the SEC, regarding interim financial reporting, and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. These condensed consolidated financial statements include the accounts of C4 Therapeutics, Inc. and its subsidiary C4T Securities Corporation. All intercompany balances and transactions have been eliminated in consolidation. Marketable securities The Company classifies marketable securities with a remaining maturity when purchased of greater than three months as available-for-sale. Marketable securities with a remaining maturity date greater than one year are classified as non-current assets. Available-for-sale securities are carried at fair value with the unrealized gains and losses included in accumulated other comprehensive income as a component of stockholders’ equity (deficit) until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the instrument. Realized gains and losses are determined using the specific identification method and are included in other income (expense). Unaudited interim financial information The accompanying condensed consolidated balance sheet as of March 31, 2021, the condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020, the condensed consolidated statements of stockholders’ equity (deficit) for the three months ended March 31, 2021 and 2020, the condensed consolidated statements of cash flows for the three months ended March 31, 2021 and 2020, and the related interim disclosures are unaudited. These unaudited condensed consolidated financial statements include all adjustments necessary, consisting of only normal recurring adjustments, to fairly state the financial position and the results of the Company’s operations and cash flows for interim periods in accordance with U.S. GAAP. Interim period results are not necessarily indicative of results of operations or cash flows for a full year or any subsequent interim period. The accompanying condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements as of and for year ended December 31, 2020, and notes thereto, which are included in the Company’s Annual Report on Form 10-K that was filed with the SEC on March 11, 2021. Significant accounting policies The Company’s significant accounting policies are disclosed in the audited consolidated financial statements for the year ended December 31, 2020, which are included in the Company’s Annual Report on Form 10-K that was filed with the SEC on March 11, 2021. Use of estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. The Company bases its estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. This process may result in actual results differing materially from those estimated amounts used in the preparation of the condensed consolidated financial statements if these results differ from historical experience or other assumptions do not turn out to be substantially accurate, even if such assumptions are reasonable when made. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, amounts and timing of revenues recognized under the Company’s research and development collaboration arrangements and accrued research and development expense. The Company assesses estimates on an ongoing basis; however, actual results could materially differ from those estimates. Recently issued accounting standards In December 2019, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, or ASU 2019-12, which is intended to simplify various aspects related to accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The Company adopted the provisions of ASU 2019-12 effective January 1, 2021, which did not have a material effect on the Company’s condensed consolidated financial statements. In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides temporary optional guidance for a limited time to ease the potential accounting impacts associated with transitioning away from reference rates that are expected to be discontinued, such as the London Interbank Offered Rate, or LIBOR. Optional expedients in Topic 848 are generally available until December 31, 2022. The adoption of ASU 2020-04 is not expected have a material effect on the Company’s condensed consolidated financial statements.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2021

Summary of Significant Accounting Policies

Note 2. Summary of significant accounting policies

Basis of presentation and consolidation

The accompanying interim unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States, or U.S. GAAP, and applicable rules and regulations of the Securities and Exchange Commission, or the SEC, regarding interim financial reporting, and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. These condensed consolidated financial statements include the accounts of C4 Therapeutics, Inc. and its subsidiary C4T Securities Corporation. All intercompany balances and transactions have been eliminated in consolidation.

Marketable securities

The Company classifies marketable securities with a remaining maturity when purchased of greater than three months as available-for-sale. Marketable securities with a remaining maturity date greater than one year are classified as non-current assets. Available-for-sale securities are carried at fair value with the unrealized gains and losses included in accumulated other comprehensive income as a component of stockholders’ equity (deficit) until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the instrument. Realized gains and losses are determined using the specific identification method and are included in other income (expense).

Unaudited interim financial information

The accompanying condensed consolidated balance sheet as of March 31, 2021, the condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020, the condensed consolidated statements of stockholders’ equity (deficit) for the three months ended March 31, 2021 and 2020, the condensed consolidated statements of cash flows for the three months ended March 31, 2021 and 2020, and the related interim disclosures are unaudited. These unaudited condensed consolidated financial statements include all adjustments necessary, consisting of only normal recurring adjustments, to fairly state the financial position and the results of the Company’s operations and cash flows for interim periods in accordance with U.S. GAAP. Interim period results are not necessarily indicative of results of operations or cash flows for a full year or any subsequent interim period. The accompanying condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements as of and for year ended December 31, 2020, and notes thereto, which are included in the Company’s Annual Report on Form 10-K that was filed with the SEC on March 11, 2021.

Significant accounting policies

The Company’s significant accounting policies are disclosed in the audited consolidated financial statements for the year ended December 31, 2020, which are included in the Company’s Annual Report on Form 10-K that was filed with the SEC on March 11, 2021.

Use of estimates

The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. The Company bases its estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. This process may result in actual results differing materially from those estimated amounts used in the preparation of the condensed consolidated financial statements if these results differ from historical experience or other assumptions do not turn out to be substantially accurate, even if such assumptions are reasonable when made. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, amounts and timing of revenues recognized under the Company’s research and development collaboration arrangements and accrued research and development expense. The Company assesses estimates on an ongoing basis; however, actual results could materially differ from those estimates.

Recently issued accounting standards

In December 2019, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, or ASU 2019-12, which is intended to simplify various aspects related to accounting for income taxes. ASU 2019-12 removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The Company adopted the provisions of ASU 2019-12 effective January 1, 2021, which did not have a material effect on the Company’s condensed consolidated financial statements.

In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides temporary optional guidance for a limited time to ease the potential accounting impacts associated with transitioning away from reference rates that are expected to be discontinued, such as the London Interbank Offered Rate, or LIBOR. Optional expedients in Topic 848 are generally available until December 31, 2022. The adoption of ASU 2020-04 is not expected have a material effect on the Company’s condensed consolidated financial statements.