Mortgage Calculator

/* Copyright 2004 Steven Alyari . All rights reserved. Except for commify function. See copyright notice in commify function below. This file is part of Mortgage & Loan Calculator. Mortgage & Loan Calculator is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. Mortgage & Loan Calculator is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with Mortgage & Loan Calculator; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */ function isPUMonth(){ var PU = document.form.PU; if (PU[0].checked == true) { return 1; } else { return 0; } } function isBPUMonth(){ var BPU = document.form.BPU; if (BPU[0].checked == true) { return 1; } else { return 0; } } function getBaloonAmount(){ /* B: baloon amount A: monthly payment P: loan amount i: interest n: loan period b: baloon months PU: period unit: n is Y or M j : current month LP: remaining loan amount PP: loan amount paid this month II: interest paid this month Nn: months remaining sd: start date of loan py: payments per year */ if (checkForMissingData(['A', 'P', 'i', 'n'])) { return; } var A, P, i, n; var j, LP, PP, II, Nn, sd, py, B; f = document.form; A = Number(f.A.value); P = Number(f.P.value); i = Number(f.i.value); n = Number(f.n.value); b = Number(f.b.value); LP = P; Nn = n; if (!isBPUMonth()) { b = b * 12; } sd = new Date(); py = 12; for (j = 1; j <= b; j++) { sd.setMonth(sd.getMonth() + 1); II = LP * i / py / 100; LP += II; PP = A - II; LP -= A; } B = LP; return B; } function amortize(){ /* M: selected month Y: selected year A: monthly payment P: loan amount i: interest n: loan period b: baloon start month j : current month LP: remaining loan amount PP: loan amount paid this month II: interest paid this month Nn: months remaining sd: start date of loan py: payments per year */ if (checkForMissingData(['A', 'P', 'i', 'n'])) { return; } var as = window.open('loo', 'noo', 'scrollbars=yes,top=100,left=300,width=550,height=450'); var A, P, i, n, b; var j, LP, PP, II, Nn, sd, py; var txt = ''; f = document.form; M = Number(f.M.value); Y = Number(f.Y.value); A = Number(f.A.value); P = Number(f.P.value); i = Number(f.i.value); n = Number(f.n.value); b = Number(f.b.value); LP = P; if (!isBPUMonth()) { b = b * 12; } if (!isPUMonth()) { n = n * 12; } if (b) { Nn = b; } else { Nn = n; } sd = new Date(Y, M, 0, 0, 0, 0, 0); py = 12; txt += '\n \n \n Mortgage Calculator\n '; as.document.write(txt); as.document.close(); } function convertVariablesToIntegers(){ f = document.form; f.P.value = f.P.value.replace(/[^\d\.]/g, ""); f.i.value = f.i.value.replace(/[^\d\.]/g, ""); f.n.value = f.n.value.replace(/[^\d\.]/g, ""); f.A.value = f.A.value.replace(/[^\d\.]/g, ""); f.F.value = f.F.value.replace(/[^\d\.]/g, ""); f.b.value = f.b.value.replace(/[^\d\.]/g, ""); } function checkForMissingData(inputs){ for (var i = 0; i < inputs.length; i++) { input = inputs[i]; if (document.form[input].value) { continue; } else { setMissingDataError(); return 1; } } unsetMissingDataError(); return 0; } function checkForPaymentLessThanPresentValue(){ /* A: monthly payment P: loan amount */ var A, P; f = document.form; A = f.A.value; P = f.P.value; if (Number(A) > Number(P)) { setPaymentLessThanPresentValueError(); return 0; } else { unsetPaymentLessThanPresentValueError(); return 1; } } function setMissingDataError(){ e = document.getElementById('errorBox'); c = document.getElementById('requiredInputMissingError'); e.style.display = 'block'; c.style.display = 'block'; } function setPaymentLessThanPresentValueError(){ e = document.getElementById('errorBox'); c = document.getElementById('paymentLessThanPresentValueError'); e.style.display = 'block'; c.style.display = 'block'; } function unsetMissingDataError(){ e = document.getElementById('errorBox'); c = document.getElementById('requiredInputMissingError'); e.style.display = 'none'; c.style.display = 'none'; } function unsetPaymentLessThanPresentValueError(){ e = document.getElementById('errorBox'); c = document.getElementById('paymentLessThanPresentValueError'); e.style.display = 'none'; c.style.display = 'none'; } function setResults(){ /* RA,A: monthly payment RP,P: loan amount Ri,i: interest Rn,n: loan period RF,F: future value RI: interest amount RT: total amount B: baloon amount */ f = document.form; f.RA.value = convertVariableToMoney(f.A.value); f.RP.value = convertVariableToMoney(f.P.value); f.Ri.value = round(f.i.value) + '%'; var unit; if (isPUMonth()) { unit = "months"; } else { unit = "years"; } f.Rn.value = round(f.n.value) + " " + unit; f.RF.value = convertVariableToMoney(f.F.value); var A, P, r, RI, RT, B; A = f.A.value; P = f.P.value; n = f.n.value; b = f.b.value; if (!isPUMonth()) { n = n * 12; } if (b) { B = getBaloonAmount(); RT = A * b + B; } else { B = Number(0.00); RT = A * n; } RI = RT - P; f.B.value = convertVariableToMoney(B); f.RI.value = convertVariableToMoney(RI); f.RT.value = convertVariableToMoney(RT); } function commify(variable){ /* Commify function not copyright Steven Alyari. Instead: This JavaScript takes an input number and adds commas in the proper places. As needed by its original purpose, also adds a dollar. Copyright 1998, David Turley Feel free to use and build on this code as long as you include this notice. Last Modified March 3, 1998 Newly revised by Steven Alyari: 2004 */ var Num = String(variable); var newNum = ""; var newNum2 = ""; var count = 0; //check for decimal number if (Num.indexOf('.') != -1) { //number ends with a decimal point if (Num.indexOf('.') == Num.length - 1) { Num += "00"; } if (Num.indexOf('.') == Num.length - 2) { //number ends with a single digit Num += "0"; } var a = Num.split("."); Num = a[0]; //the part we will commify var end = a[1] //the decimal place we will ignore and add back later } else { var end = "00"; } //this loop actually adds the commas for (var k = Num.length - 1; k >= 0; k--) { var oneChar = Num.charAt(k); if (count == 3) { newNum += ","; newNum += oneChar; count = 1; continue; } else { newNum += oneChar; count++; } } //but now the string is reversed! //re-reverse the string for (var k = newNum.length - 1; k >= 0; k--) { var oneChar = newNum.charAt(k); newNum2 += oneChar; } // add dollar sign and decimal ending from above newNum2 = "$" + newNum2 + "." + end; return newNum2; } function convertVariablesToMonies(){ /* RA: monthly payment RP: loan amount Ri: interest Rn: loan period RF: future value RI: interest amount RT: total amount */ /* f = document.form; f.RF.value = convertVariableToMoney(f.RF.value); f.RA.value = convertVariableToMoney(f.RA.value); f.RI.value = convertVariableToMoney(f.RI.value); f.RT.value = convertVariableToMoney(f.RT.value); */ } function round(variable){ return Math.round(variable * 100) / 100; } function convertVariableToMoney(variable){ if (variable == null) { return variable; } else { variable = round(variable); variable = commify(variable); return variable; } } function solveForPayment(){ /* A: monthly payment (solving) P: loan amount i: interest n: loan period */ if (checkForMissingData(['P', 'i', 'n'])) { return; } var A, P, i, n; f = document.form; P = f.P.value; i = f.i.value / 12 / 100; n = f.n.value; if (!isPUMonth()) { pow = Math.pow(1 + i, n * 12); } else { pow = Math.pow(1 + i, n); } A = P * ((i * pow) / (pow - 1)); f.A.value = A; setResults(); } function applyNewtonRaphsonMethodForInterestRate(i, A, P, n){ /* A: monthly payment P: loan amount i: guessed interest n: loan period i2 = next guessed interst (solving) Fi: interest function Fii: interest function derivative */ var Fi, Fii, i2; Fi = 1 - (Math.pow((1 + i), (-n))) - ((P / A) * i); Fii = (n * (Math.pow((1 + i), (-n - 1)))) - (P / A); i2 = i - (Fi / Fii); return i2 } function solveForInterestRate(){ /* A: monthly payment P: loan amount i: interest (solving) n: loan period */ if (checkForMissingData(['P', 'A', 'n'])) { return; } else if (!checkForPaymentLessThanPresentValue()) { return; } var A, P, i, n; var diff, newdiff, temp; f = document.form; A = f.A.value; P = f.P.value; n = f.n.value; if (!isPUMonth()) { n = n * 12; } diff = 10000; i = 0.1; A = new Number(A); P = new Number(P); n = new Number(n); i = new Number(i); i = 0.1; for (var k = 0; k < 20; k++) { temp = i; i = applyNewtonRaphsonMethodForInterestRate(i, A, P, n); newdiff = Math.abs(i - temp); if (diff <= newdiff) { break; } diff = newdiff; } f.i.value = i * 100 * 12; setResults(); } function applyNewtonRaphsonMethod(x, p, n){ /* A,x: monthly payment P,p: loan amount i: interest (solving) n: loan period */ var k = 0; var i = new Array(); var diff, diff2; i[k] = 0.003846; for (k = 0; k < 100; k++) { // diff = Math.abs(i[k+1]-i[k]); t1 = (x * (1 - (i[k] * p / x))); t2 = (n * i[k] + Math.log(1 - (i[k] * p / x))); t3 = (((x * n) * (1 - i[k] * p / x)) - p); i[k + 1] = i[k] - ((t1 * t2) / t3); // diff2 = Math.abs(i[k+1] - i[k]); // if (diff2 > diff) { // break; // } } return i[5] * 12; } function solveForMonths(){ /* A: monthly payment P: loan amount i: interest n: loan period (solving) */ if (checkForMissingData(['P', 'i', 'A'])) { return; } else if (!checkForPaymentLessThanPresentValue()) { return; } var A, P, i, n; f = document.form; A = f.A.value; P = f.P.value; i = f.i.value / 12 / 100; n = Math.log(A / (A - (P * i))) / Math.log(1 + i); if (!isPUMonth()) { n = n / 12; } f.n.value = n; setResults(); } function solveForPresentValue(){ /* A: monthly payment P: loan amount (solving) i: interest n: loan period */ if (checkForMissingData(['A', 'i', 'n'])) { return; } var A, P, i, n; f = document.form; A = f.A.value; i = f.i.value / 12 / 100; n = f.n.value; if (!isPUMonth()) { n = n * 12; } pow = Math.pow(1 + i, n); P = (A * (pow - 1)) / (i * pow); f.P.value = P; setResults(); } function solveForFutureValue(){ /* P: loan amount i: interest n: loan period F: future value (solving) */ if (checkForMissingData(['P', 'i', 'n'])) { return; } var P, i, n, F; f = document.form; P = f.P.value; i = f.i.value / 12 / 100; n = f.n.value; if (!isPUMonth()) { n = n * 12; } pow = Math.pow(1 + i, n); F = P * pow; f.F.value = F; setResults(); } function main(arg){ switch (arg) { case 'Init': init(); break; case 'SwitchSolveFor': switchSolveForCommand(); break; case 'Solve': solveCommand(); break; case 'Amortize': solveCommand(); amortizeCommand(); break; } } var solveForInfoBoxState; function disableAmortized(){ e = document.form.M.disabled = true; e = document.form.Y.disabled = true; } function init(){ switchSolveForCommand(); setAmortizeDefaultDate(); } function setAmortizeDefaultDate(){ var date = new Date(); f = document.form; f.Y.selectedIndex = date.getYear() - 80; f.M.selectedIndex = date.getMonth(); } function switchSolveForCommand(){ var solveFor; unsetMissingDataError(); f = document.form; solveFor = f.solveFor.value; switch (solveFor) { case 'A': setSolveForPaymentInfo(); break; case 'P': setSolveForPresentValueInfo(); break; case 'i': setSolveForInterestRateInfo(); break; case 'n': setSolveForMonthsInfo(); break; case 'F': setSolveForFutureValueInfo(); break; default: break; } } function resetSetSolveForInfo(newId){ var id; if (!solveForInfoBoxState) { id = "solveForPaymentInfo"; } else { id = solveForInfoBoxState; } e = document.getElementById(id); e.style.display = "none"; solveForInfoBoxState = newId; } function setSolveForPaymentInfo(){ var id = "solveForPaymentInfo"; resetSetSolveForInfo(id); e = document.getElementById(id); e.style.display = "block"; } function setSolveForPresentValueInfo(){ var id = "solveForPresentValueInfo"; resetSetSolveForInfo(id); e = document.getElementById(id); e.style.display = "block"; } function setSolveForInterestRateInfo(){ var id = "solveForInterestRateInfo"; resetSetSolveForInfo(id); e = document.getElementById(id); e.style.display = "block"; } function setSolveForMonthsInfo(){ var id = "solveForMonthsInfo"; resetSetSolveForInfo(id); e = document.getElementById(id); e.style.display = "block"; } function setSolveForFutureValueInfo(){ var id = "solveForFutureValueInfo"; resetSetSolveForInfo(id); e = document.getElementById(id); e.style.display = "block"; } function amortizeCommand(){ amortize(); } function solveCommand(){ var solveFor; f = document.form; convertVariablesToIntegers(); solveFor = f.solveFor.value; switch (solveFor) { case 'A': solveForPayment(); break; case 'P': solveForPresentValue(); break; case 'i': solveForInterestRate(); break; case 'n': solveForMonths(); break; case 'F': solveForFutureValue(); break; default: solveForInterestRate(); break; } convertVariablesToMonies(); }