COLLABORATION AND LICENSE AGREEMENTS	6 Months Ended
COLLABORATION AND LICENSE AGREEMENTS	Jun. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
COLLABORATION AND LICENSE AGREEMENTS	COLLABORATION AND LICENSE AGREEMENTS In April 2024, the Company entered into a two-year Collaboration and License Agreement (the "Collaboration Agreement") with Johnson & Johnson, through its wholly-owned subsidiary, Momenta Pharmaceuticals, Inc. (“J&J”) to facilitate the advancement of research into products to address unmet needs relating to FNAIT. The Company has an ongoing multinational FNAIT natural history study to determine the frequency of women at higher FNAIT risk among pregnant women of different racial and ethnic characteristics, as well as the frequency of HPA-1a alloimmunization and pregnancy outcomes among these women. In this study, participants are screened to determine whether they are HPA-1a negative, positive for HLA-DRB3*01:01 and for the absence of HPA-1a alloantibodies. Subject to the results of the initial screenings, a final screening may be conducted to detect whether the fetus is HPA-1a positive. The FNAIT natural history study is expected to screen up to 30,000 pregnant women of different racial and ethnic characteristics in North America and Europe. In addition, the Company is a sponsor of a planned Phase 2 FNAIT clinical trial that will include collection of certain natural history data. Pursuant to the Collaboration Agreement, the Company received an upfront payment of $0.5 million from J&J for the information dissemination and data provision services under the agreement. In addition, the Company is eligible for payments upon the achievement of certain enrollment-related events, totaling up to $0.7 million. The Company is also eligible to receive additional payments upon certain triggers related to the companies' FNAIT studies. The Company evaluated the agreement and determined it was within the scope of ASC 606. The Company determined there were performance obligations as follows: (1) Data collection & submission revenue – derived from Rallybio’s ongoing management of the studies including the maintenance of a minimum site footprint, the license to utilize, and timely, semi-annual submission of the anonymized data, in the required formats. (2) Dissemination of J&J materials & participant revenue – derived from Rallybio’s dissemination of content, information or materials related to the J&J-Sponsored Studies that are developed by J&J and are provided by Rallybio for the purpose of disseminating such content, information, or materials to staff at Rallybio study sites to provide to potential eligible participants regarding J&J’s independent study. In April 2024, the Company also entered into a Securities Purchase Agreement with JJDC. Under the terms of the Securities Purchase Agreement, JJDC made an equity investment purchasing 3,636,363 shares of common stock with a par value of $0.0001 per share for a share purchase price of $1.82 per share which includes a 10% premium for an aggregate purchase price of $6.6 million. The Securities Purchase Agreement contains provisions related to the registration of the shares and the restriction on the sale or transfer of the shares for a period of time. The Company determined the Collaboration Agreement and Securities Purchase Agreement represented combined agreements. In accordance with ASC 606 and ASC Topic 820, Fair Value Measurement (“ASC 820”), total consideration of $1.2 million for the shares of common stock from the Securities Purchase Agreement, which represents the premium of $0.7 million and discount for lack of marketability of $0.5 million, has been allocated to revenue and will be recognized over the two year expected performance period. The Company valued the common stock issued to JJDC, in connection with the Securities Purchase Agreement at fair value. The resulting fair value of $5.4 million was determined by applying the discount due to lack of marketability during the registration and lock-up period to the public trading price of the common stock, which is a Level 1 input, on the date of sale. The Company determined the value of the lack of marketability during the registration and lock-up period by utilizing put option models, which are considered Level 3 inputs. Such option models included the Company’s historical volatility of 113.2% and the risk-free rate of 5.28% based on U.S. Treasury bond rates, as key inputs. The Company recognized $0.3 million in revenue during the three and six months ended June 30, 2024, related to data collection and data submission with the identified performance obligations, and the premium and discount allocated to revenue from the sale of the common stock to JJDC. The remaining revenue is included in deferred revenue as of June 30, 2024, and will be recognized as the performance obligations are satisfied. The Company determined that the Collaboration Agreement is not in the scope of ASC 808,Collaborative Arrangements.