I want to create a financial planning application (for personal use), for which the overall functionality will be this:

• User (me..) can create different 'scenarios'.
• Each scenario is configured with different incomings/outgoings.
• Scenarios can be 'explored' in a calendar format with projections taking into account tax, interest (on both debt and savings) and so on and so forth.

My problem lies in how to fundamentally approach the project.

I've considered:

• When creating incomings/outgoings for a script to apply them to each day in a 'days' table of a database, acting as a method of caching. This means that if I wanted to look at January 14th, 2074 there aren't thousands of cycles of calculations to run through and the result can just be pulled.
• Do each calculation dynamically, but again, I'm finding it hard to visuallize how I would handle different tax allowances (I'm based in the UK by the way), payrises and 'changes' to my incomings/outgoings.

I've sat on this for a couple of days and am struggling to come up with an elegant approach to my problem.

There may well be software out there that does what I'm looking to do (in fact I'm sure it is) but I would like to develop this myself for learning purposes, to be able to add it to my personal life 'toolset' and to allow me to expand on it in the future.

Many thanks to all who have any input on my dilemna.