FSharp.Finance.Personal
F# Finance - Personal
FSharp.Finance.Personal is a set of functions for calculating Annual Percentage Rates (APRs) and amortisation schedules for products such as personal loans, mortgages, etc.
APRs
An Annual Percentage Rate (APR) is a standardised way of calculating the cost of a financial product by extrapolating charges, interest and fees and annualising the results. The aim is to make it easier for customers to compare the cost of different products.
Calculating APRs is highly regulated. Initially this library supports three methods: the EU method as set out in Directive Directive 2008/48/EC, the UK method published by the Financial Conduct Authority (FCA) and the US Acturial method specified by the Consumer Financial Protection Bureau (CFPB).
Of the three, the EU and UK methods are currently (as of 2025-05-08) identical, but the US calculation method is the more complicated, and this library attempts to comply with the regulations as closely as possible, though sometimes the implementation requires a certain interpretation of the rules. No warranty is provided for the accuracy of the results but the library has been tested against all of the single-advance examples provided by the CFPB.
Amortisation
Amortisation is the process of gradually paying down the principal of a lending product such as a mortgage or loan, taking into account any charges, interest and fees that may arise until the product is settled (fully paid off).
This library is able to generate amortisation schedules based on a highly customisable set of parameters, taking into account scheduled payments and actual payments, calculating charges, interest and fees, producing statements showing the current progress of a product or quotes for settlement of a product.
More about this library
Compliance
Technical documents going into detail about the calculations:
Actuarial-Interest Calculations
FAQ to highlight the amortisation calculations from a business perspective:
Unit-test output
Many of the unit tests output basic schedules or amortisation schedules, along with the parameters used to create them and some initial and final stats. The output files are listed here:
Future development
The FSharp.Finance family
FSharp.Finance.Personal covers personal finance, whereas FSharp.Finance.Corporate and FSharp.Finance.Public could potentially cover other areas of finance - anyone interested!?