People's minds work in different ways.

Some can do maths very easily and use that; others find it easier to fly visually by seat of the pants. I can do mental maths or I can fly, I can't always do both.

I did a similar thing to the OP in that during my ATPL training, I programmed a Psion (remember those?) to work out hold entry and headings etc, for me - given the wind. Of course just before a critical flying test, I dropped my Psion which jogged the batteries and my program was lost !! So I was back to mental maths and ready reckoning. (I passed the test by the way !!)

Nevertheless, I found that my hold program had been very useful to help me explore how things varied with wind, and by changing one parameter I could see how every aspect of the hold changed. Having done this and worked through many examples, I understood the dynamics and I didn't need my hold program again. Later, when I flew basic BAe146s, I got very good at flying holds on the heading bug, just using the seat of my pants. Thanks to the amount of traffic trying to get into Heathrow, I had lots of manual hold practice over Ockham !

So I don't think there is a problem with the OP working out the circling approach in this way. I don't think it means they are trying to fly the perfect circling approach, I think they are just working it out in their mind.

I sat down with a piece of paper and used my remembered school trigonometry one day to work out where the 3s per 100' would actually place me, geographically, relative to the runway. A useful exercise, since I now know roughly where to turn base using visual references without doing any maths as I fly, (and this automatically takes wind into account.)

Good luck D, but don't use your spreadsheet when flying. You will become unstuck one day if you do. Just use it to explore and understand the manoeuvre.

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Dadanawa, While studying scenarios, by all means look at those that you feel "fit" into the ordinary possibilities, but do not avoid the extraordinary situations. In very high winds, the base turn might need to be commenced prior to reaching abeam the threshold, in order to remain within the circling area during the turn onto final. Timing is irrelevant if compliance results in busting the circling area.
It is no comfort to your widow that remaining within the circling area meant flight through unacceptable weather events like a microburst.
So it is not just a computer app, but aggressive animal survival instincts that can sometimes count.

Very thoughtful post. I'm working on the calculation for the point on the base leg turn to start descent. Calculated in time or bearing from threshold . Will keep you posted. I don't envisage ever using this down low. But it will help with getting the big picture.

How do you drive around an oval shaped roundabout to an exit you can't see? Don't try to calculate your route around L"Etoile in Paris wanting to take the 6th exit from your entry, where you start in the inside lane and need to drift to the outside one in time. After 3 revolutions in rush-hour traffic you throw away the TomTom and decide that dare & cunning works better.

complex subject
 

The complexity of circling can be found in the following links.
Circling Approach Survival Guide | BCA content from Aviation Week
Circling Approach Area