SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION (Policies)	6 Months Ended
Jun. 30, 2025
Accounting Policies [Abstract]
Unaudited Financial Information	Unaudited Financial Information — The unaudited condensed consolidated financial statements of the Company have been prepared in conformity with accounting principles generally accepted in the United States of America ("GAAP"), and pursuant to the rules and regulations of the Securities and Exchange Commission (the "SEC"). Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates promulgated by the Financial Accounting Standards Board. In the opinion of the Company, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the financial position and results of operations for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period. The accompanying unaudited condensed consolidated financial statements include the accounts of Rallybio Corporation and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. These accompanying unaudited condensed consolidated financial statements and notes should be read in conjunction with Rallybio's Annual Report on Form 10-K for the year ended December 31, 2024 (our "Annual Report"). The Company's significant accounting policies are described in Note 2 of the Notes to the consolidated financial statements included in our Annual Report. There have been no new accounting policies, including the adoption of new accounting standards during the three and six months ended June 30, 2025, unless otherwise noted below, which could be expected to materially impact the Company's unaudited condensed consolidated financial statements.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements—In December 2023, the Financial Accounting Standards Board ("FASB") issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures ("ASU 2023-09") which establishes new income tax disclosure requirements in addition to modifying and eliminating certain existing requirements. Public business entities must apply the ASU’s guidance to annual periods beginning after December 15, 2024. The Company has chosen not to early adopt this standard and is currently evaluating the potential impact of adopting this standard on its financial statements. In November 2024, the FASB issued ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses ("ASU 2024-03"). This ASU requires public entities to disclose additional transparency on certain costs and expenses. ASU 2024-03 is effective for annual periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027. Early adoption is permitted. The Company has chosen not to early adopt this standard and is currently evaluating the potential impact of adopting this standard on its financial statements.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION (Policies)

6 Months Ended

Jun. 30, 2025

Unaudited Financial Information — The unaudited condensed consolidated financial statements of the Company have been prepared in conformity with accounting principles generally accepted in the United States of America ("GAAP"), and pursuant to the rules and regulations of the Securities and Exchange Commission (the "SEC"). Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates promulgated by the Financial Accounting Standards Board.

In the opinion of the Company, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the financial position and results of operations for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period.

The accompanying unaudited condensed consolidated financial statements include the accounts of Rallybio Corporation and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

These accompanying unaudited condensed consolidated financial statements and notes should be read in conjunction with Rallybio's Annual Report on Form 10-K for the year ended December 31, 2024 (our "Annual

Report"). The Company's significant accounting policies are described in Note 2 of the Notes to the consolidated financial statements included in our Annual Report. There have been no new accounting policies, including the adoption of new accounting standards during the three and six months ended June 30, 2025, unless otherwise noted below, which could be expected to materially impact the Company's unaudited condensed consolidated financial statements.

Recently Issued Accounting Pronouncements

Recently Issued Accounting Pronouncements—In December 2023, the Financial Accounting Standards Board ("FASB") issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures ("ASU 2023-09") which establishes new income tax disclosure requirements in addition to modifying and eliminating certain existing requirements. Public business entities must apply the ASU’s guidance to annual periods beginning after December 15, 2024. The Company has chosen not to early adopt this standard and is currently evaluating the potential impact of adopting this standard on its financial statements.

In November 2024, the FASB issued ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses ("ASU 2024-03"). This ASU requires public entities to disclose additional transparency on certain costs and expenses. ASU 2024-03 is effective for annual periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027. Early adoption is permitted. The Company has chosen not to early adopt this standard and is currently evaluating the potential impact of adopting this standard on its financial statements.