Using all French court decisions from 2002–2014 with 6 million decisions, we estimate significant impact on sentence lengths, but mainly for those defendants present at trial—equivalent to 3.5 days reduction. The average sentence length is 95 days. Focusing on the three-month threshold (the median sentence length), defendants are 1.6% less likely to be sentenced above this threshold on their birthday. Including controls for gender, crime, age, and nationality, the effect is 1.1% and remains statistically significant at the 5% level. Disaggregating the components of the sentence length reveals the impact is greatest on probation sentences–defined as the prison sentence people get in case of violation of their probation. Notably, individuals with drug offenses—but not violent offenses—benefit from this judicial leniency. They are 5% less likely to have sentences above three-months if sentenced on their birthday and appearing at trial.
For the United States, the birthday effect shows up only for the “days” component of the sentence, not for the “months” component.