;;;; Mortgage Calculators

#|
loan amount (p)
interest rate (r)
years (t)
payments per year (n)
loan type: fixed-rate

Payment = P x (r/n) * [1+(r/n)^n * t]/(1+r/n)^n *t - 1

or

P = payment
PV = Present Value
r = rate per period
n = number of periods

P = (r(PV)) / (1-(1+r)^-n)

|#

(defun payments (loan-total rate number-of-payments)
  (/ (* rate loan-total)
	 (- 1 (expt (+ 1 rate) (* number-of-payments -1)))))
(defun monthly-payments(loan-total rate number-of-payments)
  "Number of payments in years"
  (payments loan-total (/ rate 12) (* number-of-payments 12)))
(defun payment-total-per-year (loan-total rate number-of-payments)
  (* (payments loan-total (/ rate 12) (* number-of-payments 12)) 12))