Brought to you by the good folks at Croovy.

This gem provides a handful of functions useful for working with home loans. Specifically provided are functions for calculating Internal Rate of Return (irr) and Net Present Value (npv). Both are implemented as described in Wikipedia, and using the secant method, also as described in Wikipedia.

• http://en.wikipedia.org/wiki/Internal_rate_of_return
• http://en.wikipedia.org/wiki/Net_present_value
• http://en.wikipedia.org/wiki/Secant_method

Also provided is an function for calculating the Annual Percentage Rate (apr). It is basically sugar for the irr function, making it callable like the RATE function found in a Google Docs Spreadsheet or Microsoft Excel.

• https://support.google.com/drive/table/25273?hl=en
• http://office.microsoft.com/en-us/excel-help/rate-function-HP010342819.aspx

The Finance gem uses Newton's method (while CroovyFinance uses the secant method), and as a result, CroovyFinance's results are more inline with Excel and Google Docs. In the author's experience, certain reasonable inputs, when used with the Finance gem, produced obviously incorrect results.

Add this line to your application's Gemfile:

gem 'croovy_finance'

And then execute:

$ bundle

Or install it yourself as:

$ gem install croovy_finance

irb(main):001:0> require "croovy/finance"
=> true
irb(main):002:0> CroovyFinance::Apr.new(360, 1_044.50, 238_650).calc
=> 0.0027456868896171853

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request