There is a leap day every 4 years.
Earth completes one revolution around the sun in around 365 days and 6 hours. Over a period of 4 years, the extra 6 hours from every year get added up to become an entire day (6*4=24 hours). Hence, we have a leap day/leap year every 4 years.
Earth completes one revolution precisely
365 days,
5 hours,
48 minutes,
and 45 seconds
(365.242189 days).
Ref: