Each couple is different. There is no magic number that suggests how many times you will need to have sex to get pregnant. Some women may get pregnant after one try (or without trying!) while others may take months or longer trying to conceive.
There are several factors that will contribute to your unique situation. The first factor is less to do with how often you have sex as opposed to when you have sex. Ovulation calendars and kits are readily available, and should be used to best determine when exactly during your cycle you are fertile.
Your husband’s sperm count and quality will affect how often you need to have sex to get pregnant. If he has a normal sperm count and quality, you can have sex every day you are fertile. If his sperm count or quality is marginal or low, or you fail to conceive after several cycles of this, then you may want to try every other day.
It has been suggested that you abstain for 3-5 days before you are fertile, then have sex every day beginning two days before ovulating for 3 days in a row. The only certainty to this theory is that you should have sex on your peak day.
The most important thing to remember is that sex should happen as often as you feel comfortable with. If you feel pressure to have sex every day, you may increase your stress level making conception more difficult. Discuss with your partner how often you are both comfortable having sex, and determine a frequency that is comfortable for you both.