Finance::Amortization - Simple Amortization Schedules


use Finance::Amortization

# make a new schedule

$amortization = new Finance::Amortization(principal => 100000, rate = 0.06/12, periods = 360);

# get the balance after a the twelveth period

$balance = $amortization->balance(12)

# get the interest paid during the twelfth period

$interest = $amortization->interest(12);


Finance::Amortization is a simple object oriented interface to an amortization table. Pass in the principal to be amortized, the number of payments to be made, and the interest rate per payment. It will calculate the rest on demand, and provides a few methods to ask for the state of the table after a given number of periods.

Finance::Amortization is written in pure perl and does not depend on any other modules. It exports no functions; all access is via methods called on an amortization object. (Except for new(), of course.)


$am = Finance::Amortization->new(principal => 0, rate => 0, periods => 0, compounding => 12, precision => 2);

Creates a new amortization object. Calling interface is hash style. The fields principal, rate, and periods are available, all defaulting to zero.

Compounding is a parameter which sets how many periods the rate is compounded over. Thus, if each amortization period is one month, setting compounding to 12 (the default), will make the rate an annual rate. That is, the interest rate per period is the rate specified, divided by the compounding.

So, to get an amortization for 30 years on 200000, with a 6% annual rate, you would call new(principal => 200000, periods => 12*30, rate => 0.06), the compounding will default to 12, and so the rate will work out right for monthly payments.

precision is used to specify the number of decimal places to round to when returning answers. It defaults to 2, which is appropriate for US currency and many others.


$rate_per_period = $am->rate()

returns the interest rate per period. Ignores any arguments.


$initial_value = $am->principal()

returns the initial principal being amortized. Ignores any arguments.


$number_of_periods = $am->periods()

returns the number of periods in which the principal is being amortized. Ignores any arguments.


$pmt = $am->payment()

returns the payment per period. This method will cache the value the first time it is called.


$balance = $am->balance(12);

Returns the balance of the amortization after the period given in the argument


$interest = $am->interest(12);

Returns the interest paid in the period given in the argument


This module uses perl's floating point for financial calculations. This may introduce inaccuracies and/or make this module unsuitable for serious financial applications.

Please report any bugs or feature requests to bug-finance-amortization at, or through the web interface at


Use Math::BigRat for the calculations.

Provide amortizers for present value, future value, annuities, etc.

Allow for caching calculated values.

Provide output methods and converters to various table modules. HTML::Table, Text::Table, and Data::Table come to mind.

Write better test scripts.

Better checking for errors and out of range input. Return undef in these cases.

Use a locale dependent value to set an appropriate default for precision in the new() method.


None. This entire module is in the public domain.


Nathan Wagner <>

This entire module is written by me and placed into the public domain.