--- /dev/null
+# Mortgage cost calculator
+
+A few years back whilst buying my first house I was looking for some sort of
+mortgage calculator to churn out the basics of what interest and capital I'd be
+paying off over the term of different mortgage deals available to me.
+
+I couldn't find anything, and seeing as the word "mortgage" in French pretty
+much translates to "death pledge" I though it was a good idea to get it right!
+
+So, fed up of getting the calculator out again and again I mocked up this quick
+and dirty perl script, which is essentially for just fixed interest rate deals
+but can be used to estimate tracker types too.
+
+##Parameters are:
+
+mortgage_value *-m* Value of the mortgage (i.e. Property value minus Deposit)
+arrangement_fee *-a* Any arrangement fee on the initial mortgage
+interest_rate *-i* The rate in percent of the initial mortgage deal
+interest_rate_term *-it* The term for the initial interest rate
+term *-t* The total term of the mortgage (defaults to 25 years)
+interest_rate_increase *-ii* A yearly increace for the interest rate outside of the initial fixed term
+cap_rate_increase *-ic* Cap the yearly interest increase at a particular value
+monthly_overpayment *-o* The value of any regular monthly overpayments you intend to make
+monthly_payment *-p* An amount you decide you want to pay off each month (calculated from mortgage value, rate and term otherwise)
+
+##Example usage
+
+The simplest input for the script is just a mortgage value and an interest rate; the
+script then defaults to a 25 year term at the same fixed rate. So if I wanted a house
+costing £105k with a £5k deposit with a fixed 3.2% rate (obviously this isn't much use
+but just for illustration):
+
+<pre>
+$ ./mcalc.pl -m=100000 -i=3.2
+
+Mortgage value: 100000
+Arrangement fee added on: 0
+Term: 25 year(s)
+Interest rate: 3.2% (Monthly rate = 0.00266666666666667%)
+Interest rate term: 1 years
+Initial monthly payment: 484.68
+After initial term rate jumps by: 0
+---------------------------------------
+Total mortgage value: 100000
+---------------------------------------
+
+End of year 1 Mortgage: 97345.14 Total paid: 5816.15 Total interest: 3154.21 (Rate 3.2%, Monthly Payment 484.68)
+End of year 2 Mortgage: 94433.05 Total paid: 11800.81 Total interest: 6219.02 (Rate 3.2%, Monthly Payment 498.72)
+End of year 3 Mortgage: 91426.40 Total paid: 17785.48 Total interest: 9189.02 (Rate 3.2%, Monthly Payment 498.72)
+End of year 4 Mortgage: 88322.11 Total paid: 23770.15 Total interest: 12061.12 (Rate 3.2%, Monthly Payment 498.72)
+End of year 5 Mortgage: 85117.02 Total paid: 29754.81 Total interest: 14832.14 (Rate 3.2%, Monthly Payment 498.72)
+End of year 6 Mortgage: 81807.84 Total paid: 35739.48 Total interest: 17498.81 (Rate 3.2%, Monthly Payment 498.72)
+End of year 7 Mortgage: 78391.21 Total paid: 41724.14 Total interest: 20057.73 (Rate 3.2%, Monthly Payment 498.72)
+End of year 8 Mortgage: 74863.62 Total paid: 47708.81 Total interest: 22505.40 (Rate 3.2%, Monthly Payment 498.72)
+End of year 9 Mortgage: 71221.48 Total paid: 53693.47 Total interest: 24838.21 (Rate 3.2%, Monthly Payment 498.72)
+End of year 10 Mortgage: 67461.07 Total paid: 59678.14 Total interest: 27052.44 (Rate 3.2%, Monthly Payment 498.72)
+End of year 11 Mortgage: 63578.54 Total paid: 65662.81 Total interest: 29144.22 (Rate 3.2%, Monthly Payment 498.72)
+End of year 12 Mortgage: 59569.94 Total paid: 71647.47 Total interest: 31109.59 (Rate 3.2%, Monthly Payment 498.72)
+End of year 13 Mortgage: 55431.16 Total paid: 77632.14 Total interest: 32944.44 (Rate 3.2%, Monthly Payment 498.72)
+End of year 14 Mortgage: 51157.97 Total paid: 83616.80 Total interest: 34644.53 (Rate 3.2%, Monthly Payment 498.72)
+End of year 15 Mortgage: 46746.03 Total paid: 89601.47 Total interest: 36205.49 (Rate 3.2%, Monthly Payment 498.72)
+End of year 16 Mortgage: 42190.81 Total paid: 95586.13 Total interest: 37622.79 (Rate 3.2%, Monthly Payment 498.72)
+End of year 17 Mortgage: 37487.67 Total paid: 101570.80 Total interest: 38891.77 (Rate 3.2%, Monthly Payment 498.72)
+End of year 18 Mortgage: 32631.80 Total paid: 107555.47 Total interest: 40007.62 (Rate 3.2%, Monthly Payment 498.72)
+End of year 19 Mortgage: 27618.25 Total paid: 113540.13 Total interest: 40965.36 (Rate 3.2%, Monthly Payment 498.72)
+End of year 20 Mortgage: 22441.88 Total paid: 119524.80 Total interest: 41759.86 (Rate 3.2%, Monthly Payment 498.72)
+End of year 21 Mortgage: 17097.42 Total paid: 125509.46 Total interest: 42385.81 (Rate 3.2%, Monthly Payment 498.72)
+End of year 22 Mortgage: 11579.41 Total paid: 131494.13 Total interest: 42837.75 (Rate 3.2%, Monthly Payment 498.72)
+End of year 23 Mortgage: 5882.21 Total paid: 137478.80 Total interest: 43110.02 (Rate 3.2%, Monthly Payment 498.72)
+End of year 24 Mortgage: -0.00 Total paid: 143463.46 Total interest: 43196.79 (Rate 3.2%, Monthly Payment 498.72)
+Paid off in month 12 of year 24
+
+</pre>
+
+A more useful example would be to also specify all the other usual variables,
+so lets also specify a mortgage term of 20 years, with an initial mortgage deal
+of 3.2% fixed for 3 years with a £995 arrangement fee, after the fixed deal
+ends lets assume the rate increases by 0.4% each year plateauing at 7%:
+
+<pre>
+
+$ ./mcalc.pl -m=100000 -a=995 -t=20 -i=3.2 -it=3 -ii=0.4 -ic=7
+
+Mortgage value: 100000
+Arrangement fee added on: 995
+Term: 20 year(s)
+Interest rate: 3.2% (Monthly rate = 0.00266666666666667%)
+Interest rate term: 3 years
+Initial monthly payment: 570.28
+After initial term rate jumps by: 0.4
+---------------------------------------
+Total mortgage value: 100995
+---------------------------------------
+
+End of year 1 Mortgage: 97330.02 Total paid: 6843.37 Total interest: 3168.62 (Rate 3.2%, Monthly Payment 570.28)
+End of year 2 Mortgage: 93546.03 Total paid: 13686.75 Total interest: 6217.92 (Rate 3.2%, Monthly Payment 570.28)
+End of year 3 Mortgage: 89639.16 Total paid: 20530.12 Total interest: 9144.00 (Rate 3.2%, Monthly Payment 570.28)
+End of year 4 Mortgage: 85418.81 Total paid: 27908.29 Total interest: 12289.17 (Rate 3.6%, Monthly Payment 614.85)
+End of year 5 Mortgage: 81176.36 Total paid: 35490.29 Total interest: 15614.56 (Rate 4%, Monthly Payment 631.83)
+End of year 6 Mortgage: 76885.59 Total paid: 43266.97 Total interest: 19084.74 (Rate 4.4%, Monthly Payment 648.06)
+End of year 7 Mortgage: 72519.22 Total paid: 51228.62 Total interest: 22662.55 (Rate 4.8%, Monthly Payment 663.47)
+End of year 8 Mortgage: 68048.39 Total paid: 59364.89 Total interest: 26308.62 (Rate 5.2%, Monthly Payment 678.02)
+End of year 9 Mortgage: 63442.13 Total paid: 67664.83 Total interest: 29980.80 (Rate 5.6%, Monthly Payment 691.66)
+End of year 10 Mortgage: 58666.70 Total paid: 76116.88 Total interest: 33633.55 (Rate 6%, Monthly Payment 704.34)
+End of year 11 Mortgage: 53684.93 Total paid: 84708.87 Total interest: 37217.20 (Rate 6.4%, Monthly Payment 716.00)
+End of year 12 Mortgage: 48455.39 Total paid: 93427.99 Total interest: 40677.15 (Rate 6.8%, Monthly Payment 726.59)
+End of year 13 Mortgage: 42895.27 Total paid: 102203.85 Total interest: 43860.45 (Rate 7%, Monthly Payment 731.32)
+End of year 14 Mortgage: 36933.21 Total paid: 110979.71 Total interest: 46639.47 (Rate 7%, Monthly Payment 731.32)
+End of year 15 Mortgage: 30540.14 Total paid: 119755.57 Total interest: 48984.98 (Rate 7%, Monthly Payment 731.32)
+End of year 16 Mortgage: 23684.93 Total paid: 128531.43 Total interest: 50865.63 (Rate 7%, Monthly Payment 731.32)
+End of year 17 Mortgage: 16334.14 Total paid: 137307.29 Total interest: 52247.83 (Rate 7%, Monthly Payment 731.32)
+End of year 18 Mortgage: 8451.97 Total paid: 146083.15 Total interest: 53095.54 (Rate 7%, Monthly Payment 731.32)
+End of year 19 Mortgage: 0.00 Total paid: 154859.01 Total interest: 53370.13 (Rate 7%, Monthly Payment 731.32)
+
+</pre>
+
+Lets now assume we manage to make a £75 overpayment each month:
+
+<pre>
+
+$ ./mcalc.pl -m=100000 -a=995 -t=20 -i=3.2 -it=3 -ii=0.4 -ic=7 -o=75
+
+Mortgage value: 100000
+Arrangement fee added on: 995
+Term: 20 year(s)
+Interest rate: 3.2% (Monthly rate = 0.00266666666666667%)
+Interest rate term: 3 years
+Initial monthly payment: 570.28
+After initial term rate jumps by: 0.4%
+Cap rate jumps at: 7%
+---------------------------------------
+Total mortgage value: 100995
+---------------------------------------
+
+End of year 1 Mortgage: 96416.70 Total paid: 6843.37 Total interest: 3152.87 (Rate 3.2%, Monthly Payment 570.28 Overpayment 75.00)
+End of year 2 Mortgage: 91689.74 Total paid: 13686.75 Total interest: 6156.67 (Rate 3.2%, Monthly Payment 570.28 Overpayment 75.00)
+End of year 3 Mortgage: 86809.27 Total paid: 20530.12 Total interest: 9006.56 (Rate 3.2%, Monthly Payment 570.28 Overpayment 75.00)
+End of year 4 Mortgage: 81807.16 Total paid: 27675.37 Total interest: 12034.69 (Rate 3.6%, Monthly Payment 595.44 Overpayment 75.00)
+End of year 5 Mortgage: 76827.39 Total paid: 34936.78 Total interest: 15199.74 (Rate 4%, Monthly Payment 605.12 Overpayment 75.00)
+End of year 6 Mortgage: 71848.12 Total paid: 42296.84 Total interest: 18462.27 (Rate 4.4%, Monthly Payment 613.34 Overpayment 75.00)
+End of year 7 Mortgage: 66847.77 Total paid: 49736.84 Total interest: 21781.92 (Rate 4.8%, Monthly Payment 620.00 Overpayment 75.00)
+End of year 8 Mortgage: 61804.83 Total paid: 57236.81 Total interest: 25117.09 (Rate 5.2%, Monthly Payment 625.00 Overpayment 75.00)
+End of year 9 Mortgage: 56697.73 Total paid: 64775.21 Total interest: 28424.56 (Rate 5.6%, Monthly Payment 628.20 Overpayment 75.00)
+End of year 10 Mortgage: 51504.80 Total paid: 72328.74 Total interest: 31659.20 (Rate 6%, Monthly Payment 629.46 Overpayment 75.00)
+End of year 11 Mortgage: 46204.32 Total paid: 79871.84 Total interest: 34773.55 (Rate 6.4%, Monthly Payment 628.59 Overpayment 75.00)
+End of year 12 Mortgage: 40774.90 Total paid: 87376.02 Total interest: 37717.53 (Rate 6.8%, Monthly Payment 625.35 Overpayment 75.00)
+End of year 13 Mortgage: 35166.64 Total paid: 94760.84 Total interest: 40361.39 (Rate 7%, Monthly Payment 615.40 Overpayment 75.00)
+End of year 14 Mortgage: 29152.97 Total paid: 102145.67 Total interest: 42597.47 (Rate 7%, Monthly Payment 615.40 Overpayment 75.00)
+End of year 15 Mortgage: 22704.57 Total paid: 109530.50 Total interest: 44396.29 (Rate 7%, Monthly Payment 615.40 Overpayment 75.00)
+End of year 16 Mortgage: 15790.02 Total paid: 116915.33 Total interest: 45726.22 (Rate 7%, Monthly Payment 615.40 Overpayment 75.00)
+End of year 17 Mortgage: 8375.61 Total paid: 124300.16 Total interest: 46553.39 (Rate 7%, Monthly Payment 615.40 Overpayment 75.00)
+End of year 18 Mortgage: 425.21 Total paid: 131684.99 Total interest: 46841.45 (Rate 7%, Monthly Payment 615.40 Overpayment 75.00)
+End of year 19 Mortgage: -262.71 Total paid: 132300.39 Total interest: 46839.92 (Rate 7%, Monthly Payment 615.40 Overpayment 75.00)
+Paid off in month 1 of year 19
+
+</pre>
+
+Apparently that 75 quid overpayment brings down the compulsory payments in the,
+second half of the term by £100 and shaves a year off the mortage term.
+
+Revisiting this script again now a few years later I could still sit here plugging
+in different variables and seeing how it affects the payments in ways I'd never have
+thought of otherwise. I also notice it's far from the greatest example of perl
+scripting ever; if I ever get time I'll rewrite it.
--- /dev/null
+#!/usr/bin/perl
+
+# Glyn Astill <glyn@8kb.co.uk> 11/10/2011
+
+use strict;
+use Getopt::Long qw/GetOptions/;
+Getopt::Long::Configure('no_ignore_case');
+
+my $debug = 0;
+my $USAGE = '-m <mortgage value> -a <arrangement fee> -i <interest rate>';
+
+my $mortgage_value;
+my $arrangement_fee;
+my $interest_rate;
+my $interest_rate_term;
+my $monthly_payment;
+my $term;
+my $interest_rate_increase;
+my $cap_rate_increase;
+my $monthly_overpayment;
+
+my $year;
+my $month;
+
+my $total_mortgage;
+my $monthly_interest;
+my $month_value;
+my $total_paid;
+my $interest_accrued;
+
+##http://www.perl.com/doc/manual/html/lib/Getopt/Long.html
+use vars qw{%opt};
+die $USAGE unless
+ GetOptions(\%opt,
+ 'mortgage_value|m=n',
+ 'arrangement_fee|a=n',
+ 'interest_rate|i=f',
+ 'interest_rate_term|it=n',
+ 'term|t=n',
+ 'interest_rate_increase|ii=f',
+ 'cap_rate_increase|ic=f',
+ 'monthly_overpayment|o=n',
+ 'monthly_payment|p=n',
+ )
+ and keys %opt
+ and ! @ARGV;
+
+## initial call ... $ARGV[0] and $ARGV[1] are the command line arguments
+
+$mortgage_value = $opt{mortgage_value};
+$arrangement_fee = ($opt{arrangement_fee} // 0);
+$interest_rate = ($opt{interest_rate} // 5);
+$interest_rate_term = ($opt{interest_rate_term} // 1);
+$monthly_payment = ($opt{monthly_payment} // 0);
+$term = ($opt{term} // 25);
+$interest_rate_increase = ($opt{interest_rate_increase} // 0);
+$cap_rate_increase = $opt{cap_rate_increase};
+$monthly_overpayment = ($opt{monthly_overpayment} // 0);
+
+$total_mortgage = $mortgage_value+$arrangement_fee;
+$monthly_interest = ($interest_rate/100)/12;
+
+$month_value = $total_mortgage;
+if (! $monthly_payment) {
+ $monthly_payment = (($month_value*$monthly_interest)/(1-((1+$monthly_interest)**($term*12*-1))));
+}
+
+print "\nMortgage value: ",$mortgage_value,"\n";
+print "Arrangement fee added on: ",$arrangement_fee, "\n";
+print "Term: ", $term, " year(s)\n";
+print "Interest rate: ",$interest_rate, "% (Monthly rate = ", $monthly_interest, "%)\n";
+print "Interest rate term: ",$interest_rate_term, " years\n";
+print "Initial monthly payment: ", sprintf("%.2f", $monthly_payment) ,"\n";
+print "After initial term rate jumps by: ",$interest_rate_increase,"%\n";
+print "Cap rate jumps at: ",$cap_rate_increase,"%\n" if ($cap_rate_increase);
+print "---------------------------------------\n";
+print "Total mortgage value: ",$total_mortgage,"\n";
+print "---------------------------------------\n\n";
+
+do_it: {
+ for ($year = 1; $year < $term; $year++) {
+ if ($year > $interest_rate_term) {
+ if ((! $cap_rate_increase) || ($interest_rate < $cap_rate_increase)) {
+ $interest_rate = $interest_rate + $interest_rate_increase;
+ if ($interest_rate < 0) {
+ $interest_rate=0.0000000001;
+ }
+ elsif ($cap_rate_increase && ($interest_rate > $cap_rate_increase)) {
+ $interest_rate = $cap_rate_increase;
+ }
+ $monthly_interest = ($interest_rate/100)/12;
+ $monthly_payment = (($month_value*$monthly_interest)/(1-((1+$monthly_interest)**(($term-$year)*12*-1))));
+ }
+ }
+
+ for ($month = 1; $month <= 12; $month++) {
+ $month_value = $month_value+($month_value*$monthly_interest)-($monthly_payment+$monthly_overpayment);
+ $total_paid = $total_paid + $monthly_payment;
+ $interest_accrued = $interest_accrued + ($month_value*$monthly_interest);
+ if (($month == 12) || ($month_value <= 0)){
+ print "End of year ", pack("A5",$year);
+ print "Mortgage: ", pack("A11",sprintf("%.2f", $month_value));
+ print "Total paid: ", pack("A11", sprintf("%.2f", $total_paid));
+ print "Total interest: ", pack("A11", sprintf("%.2f", $interest_accrued));
+ print " (Rate ", $interest_rate, "%, Monthly Payment ", sprintf("%.2f", $monthly_payment);
+
+ if ($monthly_overpayment > 0) {
+ print " Overpayment ", sprintf("%.2f", $monthly_overpayment);
+ }
+
+ print ")\n";
+
+ if ($month_value <= 0) {
+ print "Paid off in month ", $month, " of year ", $year, "\n";
+ last do_it;
+ }
+
+ }
+ }
+ }
+ }
+
+__END__
projects / playtime / mortgage_calculator / commitdiff