Use commas to separate off the thousands and millions in compound numbers.
Example: 3,460,759
Don’t use commas in decimals.
Example: $3.49
Use a comma before the year if the date is given as follows: month, day, year.
Example: April 16, 2003
Don’t use a comma if only two elements of the date are given (e.g. month and year).
Example: I was born in May 1972.