There is very little evidence on the number of people who have detransitioned.
In a study  of 100 detransitioners, only 24% of respondents informed their clinicians that they had detransitioned. The vast majority made no attempt to contact their clinics.
Not only does this mean that we have no way of ascertaining how many people detransition, it also potentially impact clinics’ assessments of patient satisfaction.
One paper  claimed that the detransition rate was 13.1%. However, this research relies on data from the U.S. Transgender Survey, which was conducted via community outreach organizations, and may therefore have excluded detransitioners who were no longer in touch with any such organizations. Only people who still identified as members of the trans community were included:
The 2015 U.S. Transgender Survey (USTS) was conducted by the National Center for Transgender Equality (NCTE) to examine the experiences of transgender adults in the United States.
By contrast, the study by Lisa Littman  sought respondents from a political and ideological variety of sources.
In a recent retrospective case-note review , performed as a service evaluation over twelve months, 6.9% of participants met the case definition of detransitioning, yet 21.7% disengaged from the study.
In general, detransitioners remain an underserved population in healthcare, with far more research required to understand their needs .
 Littman, L. (2021). Individuals Treated for Gender Dysphoria with Medical and/or Surgical Transition Who Subsequently Detransitioned: A Survey of 100 Detransitioners. Arch Sex Behav. [Link]
 Turban, J.L., Loo, S.S., Almazan, A.N., & Keuroghlian, A.S. (2021). Factors Leading to “Detransition” Among Transgender and Gender Diverse People in the United States: A Mixed-Methods Analysis. LGBT health 8(4): 273-280. [Link]
 Hall, R., Mitchell, L., & Sachdeva, J. (2021). Access to care and frequency of detransition among a cohort discharged by a UK national adult gender identity clinic: Retrospective case-note review. BJPsych Open 7(6): E184. [Link]
 Expósito-Campos, P. (2021). A Typology of Gender Detransition and Its Implications for Healthcare Providers. Journal of Sex & Marital Therapy 47 (3): 270-280. [Link]