R/mortgage.R

In meryem11/MortgageP: Mortgage amortization table

#' @return dataframe of monthly payment
#'
#' @example mortgage(100000,30,0.05)
#'
#' @description The package has one function that returns an amortization table that lists monthly payment on a mortgage loan based on a loan amount, duration of loan in years, and annual interest rate. The table will provide the breakdown of the payment by how much is allocated to interest and the loan principal. It will also list the loan balance for each month.
#'
#'@export

mortgage<- function(loan_amt, years, APR) {
  # calculate simple monthly rate
  monthly_rate = APR / 12
  # calculate loan term in months
  term = years*12

  # calculate (constant) contractual monthly payment amount

  r = (1 + monthly_rate) ^ term - 1
  payment = loan_amt * monthly_rate * (r + 1) / r

  # initialize output variables
  interest = principal = balance = vector("numeric", term)

  # calc amortization schedule
  outstanding_principal = loan_amt
  for (i in 1:term) {
    intr = outstanding_principal * monthly_rate
    prnp = payment - intr
    outstanding_principal = outstanding_principal - prnp

    interest[i]  = round(as.numeric(intr),0)
    principal[i] = round(as.numeric(prnp),0)
    balance[i] = round(as.numeric(outstanding_principal),0)
  }
  #return(outstanding_principal)
  data.frame(month = 1:term, interest, principal, balance)

}