The numbers depend on a lot of factors, some of which you can control
     others of which you can't.  You could get from a few to several hundred
     free swimming fry.  These first numbers won't go up but can go down, 
     So care must be taken.  There are two good articles about breeding 
     bettas, in that section of the page.  Water conditions must be very 
     good, and food should be fed at least 3 times a day if not as many
     as 5 times a day, a little at a time.  Live foods are the best.