The minimum amount of nursing bras you should own is three. One to wash, one to wear, and one on standby. If you have the funds, the best choice would be to have three sleep nursing bras, three lounge nursing bras, and three going-out-in-public nursing bras. Not everyone can afford nine bras for a year. But if money isn't an issue, nine nursing bras will ensure comfort and always have a clean bra on standby. More often than you think, you will have to change your bra because of leaking. Even with breast pads, you will inevitably leak through.  I would suggest always having a nursing cover handy as it can cover up leaks until you can change nursing bras. Read here for the best nursing covers.