// format floating point number to show dollars and cents function currency2str(f) { var str = ""; var pos = 1; if (f < 0) // negative number { f = -f pos = 0; } // extract dollars and cents var dollars = Math.floor(f); var cents = Math.round(100*(f - dollars)); if (cents == 100) { dollars += 1; cents = 0; } if (pos == 0) str += "("; // show as negative if (cents == 0) str += dollars + ".00"; else if (cents < 10) str += dollars + ".0" + cents; else str += dollars + "." + cents; if (pos == 0) str += ")"; // show as negative return str; } // compute the size of a periodic payment to amortize a loan function monthly_payment( p, apr, n ) { var i = apr/1200; var m = p*i*Math.pow((1 + i), n)/(Math.pow((1 + i), n) - 1); return (0.01*Math.ceil(100*m)); // round up } // total interest and payment size for a loan function compute1() { var calc = document.getElementById("calc") var principal = parseFloat(calc.principal.value); var int_rate = parseFloat(calc.interestrate.value); var months1 = parseInt(calc.months1.value); var payment = monthly_payment( principal, int_rate, months1 ); var interest = parseFloat("0"); // compute total interest paid while (principal > 0.0) { var ip = 0.01*Math.round(principal*int_rate/12); principal = principal + ip - payment; interest += ip; } calc.payment.value = currency2str(payment); calc.interest1.value = currency2str(interest); } // interest and principal of each payment in a separate window function listing1() { var calc = document.getElementById("calc") var principal = parseFloat(calc.principal.value); var int_rate = parseFloat(calc.interestrate.value); var months1 = parseInt(calc.months1.value); var payment = monthly_payment( principal, int_rate, months1 ); var count = parseInt("0"); msgWindow=window.open("","msgWindow","toolbar=no,status=no,menubar=yes,scrollbars=yes,width=550,height=400"); msgWindow.document.open(); msgWindow.document.writeln("Principal and interest listing"); msgWindow.document.writeln(""); msgWindow.document.writeln("
"); msgWindow.document.writeln("Payment = $" + currency2str(payment)); msgWindow.document.writeln(''); msgWindow.document.writeln(""); while (principal > 0.0) { var ip = 0.01 * Math.round(principal*int_rate/12); if (payment > principal + ip) payment = principal + ip; var pp = payment - ip; var principal = principal + ip - payment; count++; msgWindow.document.write(""; msgWindow.document.write(""); msgWindow.document.write(""); msgWindow.document.write(""); msgWindow.document.writeln(""); } msgWindow.document.write("
MonthPrincipalInterestBalance
"); msgWindow.document.write(count) + "" + currency2str(pp) + "" + currency2str(ip) + "" + currency2str(principal) + "
"); msgWindow.document.write(""); msgWindow.document.close(); } // number of payments and total interest with extra principal function compute2() { var calc = document.getElementById("calc") var principal = parseFloat(calc.principal.value); var int_rate = parseFloat(calc.interestrate.value); var months1 = parseInt(calc.months1.value); var payment = monthly_payment( principal, int_rate, months1 ); var extra = parseFloat(calc.extra.value); var interest = parseFloat("0"); var count = parseInt("0"); if (isNaN(extra)) extra = parseFloat("0"); while (principal > 0.0) { var ip = 0.01*Math.round(principal*int_rate/12); principal = principal + ip - (payment + extra); interest += ip; count++; } calc.payment.value = currency2str(payment); calc.interest2.value = currency2str(interest); calc.months2.value = count; } // interest and principal of each payment in a separate window function listing2() { var calc = document.getElementById("calc") var principal = parseFloat(calc.principal.value); var int_rate = parseFloat(calc.interestrate.value); var months1 = parseInt(calc.months1.value); var payment = monthly_payment( principal, int_rate, months1 ); var extra = parseFloat(calc.extra.value); var count = parseInt("0"); if (isNaN(extra)) extra = parseFloat("0"); msgWindow=window.open("","msgWindow","toolbar=no,status=no,menubar=yes,scrollbars=yes,width=550,height=400,resizable=yes"); msgWindow.document.open(); msgWindow.document.writeln("Principal and interest listing"); msgWindow.document.writeln(""); msgWindow.document.writeln("
"); msgWindow.document.writeln("Payment = $" + currency2str(payment) + " + " + currency2str(extra)); msgWindow.document.writeln(''); msgWindow.document.writeln(""); while (principal > 0.0) { var ip = 0.01 * Math.round(principal*int_rate/12); // last payments if (payment > principal + ip) { payment = principal + ip; extra = 0.0; } else if (extra > principal + ip - payment) extra = principal + ip - payment; var pp = (payment + extra) - ip; var principal = principal + ip - (payment + extra); count++; msgWindow.document.write(""; msgWindow.document.write(""); msgWindow.document.write(""); msgWindow.document.write(""); msgWindow.document.writeln(""); } msgWindow.document.write("
MonthPrincipalInterestBalance
"); msgWindow.document.write(count) + "" + currency2str(pp) + "" + currency2str(ip) + "" + currency2str(principal) + "
"); msgWindow.document.write(""); msgWindow.document.close(); }