Very basic script in Ruby to calculate mortgage payments.

mortgageCalc.rb

print "enter loan amount: "
loan = gets.chomp.to_i
print "Enter length of time in months: "
time = gets.chomp.to_i
print "Enter interest rate: "
rate = gets.chomp.to_f/100

i = (1+rate/12)**(12/12)-1
annuity = (1-(1/(1+i))**time)/i 

payment = loan/annuity

puts "\n$%.2f per month" % [payment]