Ted, Marshall, and Lily were all born in 1978:- All three are portrayed as incoming college freshmen in flashbacks set in 1996.- Lily's senior prom in "Best Prom Ever" took place in 1996.- "How I Met Everyone Else" establishes that Lily, Ted and Marshall graduated from Wesleyan in 2000.- Ted turns 30 in "The Goat" (set in 2008) and 31 in "The Leap" (set in 2009). "The Goat" establishes his birthday as April 25, though "The Leap" ostensibly takes place in May.- Lily turns 32 in "Say Cheese" (set in 2010). This makes her older than Ted by a few months, though dialogue in "The Goat" seemed to imply that she and Marshall had not turned 30 yet. In "The Front Porch" Ted yells at Lily for breaking up him and Robin, and says, "You met the love of your life in a dorm hallway when you were 18." Lily went off to college in 1996, and met Marshall, placing her birth year as 1978.- In "The Yips," Marshall says he is 29. This episode aired in November 2007. This places Marshall's birth year around 1978 or 1977.Barney was born in 1976. "Game Night," which flashes back to 1998, shows Barney intending to leave for the Peace Corps, which means he was probably out of college by then; In "Columns," set in 2007, Barney gives his age as 31. "Zoo or False" further confirms that he was born seven years after the first moon landing in 1969.Robin was born in 1980. "Robin 101," set in 2009, establishes her birthdate as July 23 and gives her age at the time as 29.The Mother was born in 1984. "How Your Mother Met Me" establishes that the day Marshall and Lilly got engaged and Ted met Robin (both of which occurred in the pilot episode, which the newer episode established to take place in September of 2005) was the day of her 21st birthday.
In the first season, the font used was Century; from the second season onward (and on the DVD packaging of the first season), the typeface is Dax.