Days in Month Calculator
Every month has a fixed number of days — 31, 30, or 28/29 — determined by the Gregorian calendar rules. January, March, May, July, August, October, and December have 31 days; April, June, September, and November have 30 days; and February has 28 days in a common year or 29 days in a leap year.
A leap year occurs when the year is divisible by 4, except for century years (divisible by 100), which must also be divisible by 400 to qualify. This calculator instantly tells you how many days are in any given month and year, and displays a handy overview table of all 12 months for that year with February correctly adjusted for leap years.
How it works
Days in February = 29 if (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0, else 28. All other months follow fixed values: Jan/Mar/May/Jul/Aug/Oct/Dec = 31 days; Apr/Jun/Sep/Nov = 30 days.
Use cases
- Planning project deadlines and sprint durations for a specific month
- Calculating payroll, billing cycles, or subscription lengths accurately
- Verifying whether February has 28 or 29 days for a given year
- Building calendar applications or date-range features
- Settling date-related disputes or trivia questions quickly