Building a calculator site that doesn't cut corners on accuracy — would love your input

Hey everyone

I'm Hamza, an Algorithm Architect and Software Developer with 15+ years building financial, scientific, and engineering software professionally. I'm launching Zen Calculators soon — a free platform with 1,300+ calculators spanning finance, health, math, engineering, construction, statistics, and more.

Here's the problem I kept running into: most calculator sites treat calculators as disposable SEO content — churned out fast, rarely double-checked, with no real process for catching a wrong formula. When you're calculating a mortgage payment or a dosage conversion, "probably right" isn't good enough.

So I built Zen Calculators differently:

• Every calculator is built on standard, recognized formulas — nothing invented

• Each one is hand-tested against known example calculations, including edge cases (zero, negative, extreme values) before it ever goes live

• Every calculator has a Report Issue button that I personally review — no ticket goes into a void

• Every page shows a "last updated" date so you know how current it is

I'd love this community's input before launch:

1. What calculator have you used online that gave you a result you didn't trust — and why?

2. Are there calculator categories you feel are consistently underserved or poorly built (industry-specific, niche academic, etc.)?

3. What would actually make you trust a calculator site enough to bookmark it?

Really looking forward to hearing what this community thinks — feedback here will directly shape what I prioritize before and after launch.