How many days before you ovalate do you try to get pregnant with a girl?

3 days. Typically, female sperm (x) swim more slowly than male (y). But they live longer. So to increase the probability of a girl, have sex 3 days and maybe 2 days prior to ovulation. The differences in probability is very slight. The other option is sex selection done in a doctor's office. The ejaculate is separated into mostly male and female sperm. The desired portion is then inseminated immediately with success rates close to 98%.