How often you use a breast pump depends on how often your baby feeds, your milk supply, and your schedule, says Kathleen McCue, a Maryland-based nurse practitioner and lactation consultant. However, on average, women pump 8 to 10 times a day when they need to build a supply of breast milk to feed a baby in their absence, says McCue. Maintaining a milk supply has a lot to do with your baby's size and nutritional needs, but on average, a mother should be pumping approximately 25 ounces a day when anticipating an absence for work or commitments. Try to maintain a consistent schedule with pumping that matches your baby's needs. A lactation consultant can help you determine what is right for you, says McCue.