How long will I bleed for after taking the pill?

Im going on the contraceptive pill (brand is microlite) and it's a combination pill. I'd like to know how long I will be bleeding/spotting for as I know this happens when you first take the pill. I am starting on the day of my period. I have been told bleeding can last a month and I know it's different for everyone but I'd like to hear other people's experiences!