I built a set of lightweight financial decision tools (buy vs rent, house hacking, retirement, debt payoff) after trying to model a condo purchase for my girlfriend.

Backstory: My girlfriend was looking into buying a condo, and I was trying to convey to her how the costs add up, even compared to renting. I knew from my personal experience with house-hacking in Seattle right out of college that the simple "renting is throwing money down the drain" philosophy can lead you to rush into buying properties without actually understanding the financial implications. I was having a tough time conveying this to her verbally, so I built a "house-hacking calculator" for her using Codex to visually model how investing a down payment and renting compares to buying a condo.

Once I finished that initial prototype for her, I realized I had built something more generally useful. A lot of the available financial tools online are either overly complex for decisions like this (require modeling tax brackets, classifying bonds/investment allocations, etc.), overly simplistic (just input your mortgage rate and balance, don't consider that you can reinvest proceeds after sale), and/or require you to input a bunch of contact information before you get the answers you're looking for.

There was room for a free, responsive, lightweight tool that would immediately show to you how changing variables like down payment, interest rate, and inflation rate can impact your financial standing, without requiring you to sell your contact information. Once I built the house-hacking calculator with these design philosophies in mind, I had a lot of fun expanding to other tools like retirement planning, budget allocation, debt paydown, rent vs buy, etc. It was also really rewarding when I learned how I could host my own static webpages on Cloudflare for just $10/year for the domain.

Hopefully folks find the tools useful, and I'd love feedback on any faulty assumptions, missing inputs, and other tools I should add.