Show HN: Made a CD interest for my family

It started, as many meaningful projects often do, not with a grand vision, but with a quiet frustration. I remember sitting with my aunt, a meticulous planner, as she tried to make sense of her savings. She had a small sum set aside and was looking into Certificates of Deposit, trying to find the best home for her hard-earned money. Bank websites were a maze of fine print, varying terms, and different compounding frequencies. She’d painstakingly jot down numbers, trying to compare a 3-year CD with quarterly compounding against a 5-year one with monthly compounding, all while battling the niggling fear of making a mistake. Her spreadsheet was a patchwork of formulas she wasn't entirely confident in, and the whole process left her feeling overwhelmed, not empowered.

Watching her struggle, I felt a familiar ache. I’d been there myself. The financial world, for all its talk of transparency, often felt deliberately opaque. Calculating compound interest manually, or even with basic online tools, was tedious and rarely offered the clarity needed to make truly informed decisions. You could get a number, sure, but you couldn't see the growth, compare scenarios side-by-side, or easily adjust variables to understand their impact. And the thought of inputting personal financial data into just any website always felt like a leap of faith.

That's when the idea for the CD Interest Calculator began to take root. It wasn't about building just another calculator; it was about building a tool that truly served the individual, stripping away the complexity and replacing it with clarity and confidence. I envisioned a place where my aunt, or anyone like her, could instantly plug in numbers and not just get a result, but understand it. A visual chart that showed the power of compounding over time, the subtle but significant difference a daily compounding frequency could make, or how a slightly higher rate on a longer term truly translated into dollars.

The journey wasn't without its challenges. It wasn't enough to just implement the standard compound interest formula; I wanted it to be robust, covering all the nuances: daily, monthly, quarterly, annual compounding. Then came the realization that people don't just want to calculate; they want to plan. What if you knew your target amount, but needed to figure out the interest rate required to get there? Or, a critical one, how do taxes impact your actual take-home earnings? These questions led to the development of the reverse rate and tax calculators, each designed to answer a specific, deeply felt need.

But the most crucial design principle, born from that initial moment of watching my aunt's trepidation, was privacy. It was paramount that users felt completely secure. That meant no data ever leaving their browser, no information stored on servers. Every calculation, every projection, happens right there on their device, giving them complete control and peace of mind.

Building this suite of tools has been a labor of love, driven by the belief that everyone deserves to understand their money clearly, without jargon or guesswork. It’s about empowering people to visualize their financial future, compare options with confidence, and make decisions that truly serve their goals, all from a place of genuine understanding and trust.