Summary of Significant Accounting Policies	6 Months Ended
Summary of Significant Accounting Policies	Jun. 30, 2024
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiary, Fulcrum Therapeutics Securities Corp., which is a Massachusetts subsidiary created to buy, sell, and hold securities. All intercompany transactions and balances have been eliminated. Summary of Significant Accounting Policies The significant accounting policies and estimates used in the preparation of the accompanying consolidated financial statements are described in the Company’s audited consolidated financial statements for the year ended December 31, 2023 included in the Company’s Annual Report on Form 10-K. There have been no material changes in the Company’s significant accounting policies during the six months ended June 30, 2024, except as noted below with respect to the Company's accounting policies related to collaborative arrangements. Collaborative Arrangements At contract inception, the Company analyzes its collaboration arrangements to assess whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and are exposed to significant risks and rewards dependent on the commercial success of such activities, and therefore within the scope of ASC Topic 808, Collaborative Arrangements (ASC 808). This assessment is performed on an ongoing basis throughout the collaboration based on changes in the responsibilities of the parties in the arrangement. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, the Company first determines which elements of the collaboration are deemed to be within the scope of ASC 808 and which elements of the collaboration are more reflective of a vendor-customer relationship and are therefore within the scope of ASC 606, Revenue from Contracts with Customers (ASC 606). For elements of collaboration arrangements that are accounted for pursuant to ASC 808, an appropriate recognition method is determined and applied consistently, either by analogy to authoritative accounting literature or by applying a reasonable and rational policy election. The Company evaluates the income statement classification for presentation of amounts due from or owed to collaborators associated with multiple activities in a collaboration arrangement based on the nature of each separate activity. The Company made an accounting policy election to account for research and development reimbursements received from its collaboration partner that are outside of the scope of ASC 606 as a reduction of research and development expenses to best reflect the economics and nature of the transaction in the context of the unit-of-account. See Note 2, “Summary of Significant Accounting Policies”, in the Company’s audited consolidated financial statements for the year ended December 31, 2023 included in the Company’s Annual Report on Form 10-K for the Company's accounting policies for arrangements within the scope of ASC 606. Use of Estimates The preparation of financial statements in accordance with GAAP requires management to make certain 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 financial statements, and the reported amount of expenses during the reported periods. Estimates inherent in the preparation of these consolidated financial statements include, but are not limited to, estimates related to revenue recognition, accrued expenses, stock-based compensation expense, and income taxes. The Company bases its estimates on historical experience and other market specific or other relevant assumptions it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates as there are changes in circumstances, facts and experience. Actual results could differ from those estimates or assumptions. Off-Balance Sheet Risk and Concentrations of Credit Risk The Company has no significant off-balance sheet risk such as foreign exchange contracts, option contracts, or other foreign hedging arrangements. Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities, and restricted cash. The Company’s cash, cash equivalents, and restricted cash are deposited in accounts at large financial institutions. The Company believes it is not exposed to significant credit risk due to the financial strength of the depository institutions in which the cash, cash equivalents and restricted cash are held. The Company maintains its cash equivalents in money market funds that invest in U.S. Treasury securities, U.S. Treasury securities, and commercial paper. The Company’s marketable securities consist of U.S. Treasury securities, corporate bonds, and commercial paper, and potentially subject the Company to concentrations of credit risk. The Company has adopted an investment policy that limits the amounts the Company may invest in any one type of investment. The Company has not experienced any credit losses and does not believe it is exposed to any significant credit risk on these funds. Recent Accounting Pronouncements During the periods presented, the Company was not required to adopt any recently issued accounting standards. The Company does not expect any recently issued accounting standards to have a material impact on its financial statements.