Python beginner's body fat calculator
all of your functions seem to do the same thing with a different message, so why not condense them and take the message as a parameter?

def get_num(msg):
    num = None
    while num is None:
        try:
            num = float(raw_input(msg))
        except ValueError:
            print("Use a number, silly!")

    return num


and then

def output():
    x = get_num('Please give your weight (pounds): ')
    y = get_num('what is your current body fat percentage? (&gt;1): ')
    z = get_num('What is your desired body fat percentage? (&gt;1): ')
    A = (x*(y/100-z/100))/(1-z/100)
    B = x - A
    print("Your necessary weight loss is %.1f pounds, and \
your final weight will be %.1f pounds" % (A,B))
    more()


in your more function you can condense your ifs with the in operator

def more():
    again = raw_input("Calculate again? ")

    if again.lower() in ["yes", "y", "sure" , "ok", "", "okay"]:
        output()
    elif again.lower() in ["no", "n", "nah", "nope"]:
        end()
    else:
        more()