Show HN: AI helped me build this financial projector. What do I do with it? (opens in new tab)

I'm an experienced programmer, still figuring out the best way to use AI in my work. Does it replace me? (No.) Does it supplement me? (Yes.) Just how much of my work can it relieve me from doing, if any? Can it reliably take on large projects with essentially no coding from me, or is it better when I do the bulk of the coding and it supplements? So I'm exploring and experimenting.

This weekend I decided to put the AI (Gemini 2.5 Pro, via Cursor) front and center, giving it virtually all of the programming burden. I acted as project manager and architect, directing it in application design and the broad steps of implementation but leaving it to do all of the actual programming. In practice I had to intervene a couple of times, either to quickly edit a bit of sloppiness that was easier to fix than to explain or to debug erroneous behaviors that needed browser dev tool access to figure out. The AI couldn't have done it without me, but it did 95% of it and only got stuck three or four times. Almost all of the actual code—the "typing"—was done by Gemini.

The project was a financial project for use in planning family finance. Given your career plans (salary, retirement, savings, etc), retirement spending needs, predictions about inflation and investment return rates, etc, are you saving enough for retirement? Useful tool, no doubt, and although there are other calculators out there I couldn't find one that gave me direct access to what I wanted to control or observe. I wanted a Monte Carlo simulator that didn't just give one year-by-year prediction but that ran any number of randomized predictions—thousands—and told me not merely "you'll be fine/you won't be fine" but "you'll be fine X% of the time."

The resulting "web app" is ugly but functional. Is it correct? My testing suggests that it's reasonably correct; my reading of the AI-generated code suggests it's reasonably correct. Is it useful? I think so. Personally I find it very useful, and the more I become convinced it's correct the more useful I'll find it.

https://www.jeffwofford.com/fin_projector/

What do you think? I suppose there are a couple of avenues of question here. (1) What do you think about this kind of AI-partnering process. Tried it? Trust it? Love it? Hate it? (2) What do you think about this app? Worth my developing it further? See any errors? Do you find it useful? How might I package it to be more broadly valuable for folks?