Because >! Your child was born on June 20th. >! Last year (2015), Father's Day was June 21st, so you celebrated it the day after your child was born. >! Since 2016 is a leap year, Father's Day was on the 19th, not the 20th, so you celebrated Father's Day the second time before your child turned 1. Alternatively, >! Father's Day is the third Sunday in June, so on some years it jumps back 6 days instead of 1 (when June 1st becomes a Sunday again). >! This would also allow for a scenario similar to the previous one to happen, but didn't specifically happen recently as described in the question.