Mortgage Calculator

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 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( ); }