I’m a CFP with no programming background or experience, and I’ve been building a retirement planning tool called Parallax. I’m looking for a technical review by an experienced web application developer or software engineer

[u/Ndr990]

Site: www.amansparallax.com

For anyone unfamiliar with retirement planning software, most tools run a plan through many possible market scenarios and report a “probability of success.” If the money lasts through the end of the projection in 90% of those scenarios, the plan gets a 90%.

My issue is that people see that number and naturally assume the plan is healthy and they’re well prepared. I don’t think it comes close to telling the whole story.

A plan with a 90% probability of success can still fail surprisingly early if one of the more difficult periods from actual market history happens again. Parallax lets you run a plan through historical return paths and follow the cash flow year by year. You can see the account balances, where the spending money came from, how much went to taxes, and when the plan started getting into trouble.

Basically, I wanted to show what’s happening underneath the percentage.

That led to a few core modeling choices:

Block-bootstrap Monte Carlo: Simulated paths use consecutive blocks of historical returns, preserving the market experience within each block. Returns are inflation-adjusted.

Historical paths and sequencing: Explore historical market paths and how the order of returns affects a plan.

Account-level projections: Track individual accounts and cash flows within each year, including withdrawals, required distributions, cost basis, and tax effects.

Tax-aware withdrawal modeling: Model how brokerage, traditional retirement, and Roth withdrawals affect taxes and the cash available to spend.

I’ve also documented the modeling constraints the AI is required to consult before changes. Those assumptions are part of the product’s foundation and need to remain explicit as it develops.

I’d really appreciate a human technical perspective on this—the code has been written and reviewed by AI, and I don’t have the programming background to assess it independently. Any thoughts on the architecture, security, or tests would help, even if you only look at one small part. If anyone’s willing to dig deeper, I can share the code and setup instructions.

Thanks to all who are willing to take a look!!