Haircuts on Lag Ba'omer

 Shalom! 

 Thank you for your question. 

 The Rema states that the Ashkenazic custom permits taking a haircut on Lag B’Omer, however, he adds that one must wait until Lag B’Omer day and one should not take a haircut on the preceding evening. 

 The Mishna Berura, however cites the opinions of the Elya Rabba and the Chok Yaakov who bother permit taking a haircut on the night of Lag Ba’omer. 

 The dispute between those who allow haircuts at night, and those who only allow haircuts by day, revolves around the question of whether the rule of “a partial day counts as a full day” applies at night or only during the daytime. For example, the last day of “Shiva” ends in the morning of the seventh day of morning because having mourned “a partial day” counts as a full day, thereby ending the Shiva period in the morning. Some say that on Lag Ba’omer “a partial day counts as a full day” is like “Shiva” which would only allow haircuts on Lag Ba’omer day, while some rule that “a partial day counts as a full day” is valid on Lag Ba’omer night. 

 There is also a view that the Rema himself might have allowed haircuts after dark on the night of Lag Ba’omer but just doesn’t allow them immediately after sunset. 

 Le'halcha the custom is to wait until Lag Ba’omer morning to get a haircut. 

 OC 493 and commentaries, Yehuda Yaaleh 2:39