def main():
    while True:

        print("Welcome to the Tax  Calculator")
        first_name = (input("Please enter your first name: "))
        income = float(input("Please enter your monthly income: "))

        if income < 1000:
            print(first_name + ", you have no withholding this month.")
            if income == 0:
                break
        elif income < 2000:
            tax = 15.50
        elif income < 3000:
            tax = 50.25
        elif income < 4000:
            tax = 105.25
        elif income >= 4000:
            tax = income * .04
            print(first_name + ", your estimated monthly withholding will be: $") + str(format(tax, '.2f'))
        cmd = input('Do you want to quit? Enter \'0\'!')
        if cmd == '0':
            break

        print("Press 'Enter' to close program")

main()