How will I know that my baby needs to burp?

I'll make sure I Burp my baby all the time even after breastfeeding. The gas swallowed isn't that much as compared to bottle feeding (I sometimes supplement with formula milk). Having said that, if baby falls asleep before burping, I'll make sure she sits upright for at least 20 min or more after feeding to avoid milk being brought up again. Another alternative is letting her to sleep on her tummy. Sleeping this way will help the gas to be brought up easier relatively.