Okay, so here is the only old-wives tale that worked on me...
take your age at conception+month you concieved= odd(boy), even(girl)
Both of my boys were concieved on odd months, so needless to say DH and I will be :ttcgirl: on my projected "even" months!!!
(and if your birthday falls as your conception month... take how old you are at O day) - this happened to me with ds2