The number of days in a month varies depending on the month and the year. The following months have [katex] 31 [/katex] days: January, March, May, July, August, October and December. The following months have [katex] 30 [/katex] days: April, June, September, and November. The month of February has [katex] 28 [/katex] days, except during a leap year, where it has [katex] 29 [/katex] days.