Honestly, the reason I built this is simple. I was looking for a web monetization opportunity.
Anniversary calculators are everywhere. But when I actually used them, every single one was lacking. Year counts were wrong, designs were stuck in 2010, or holiday info was missing. I figured I could do at least as well myself.
What I Built
Enter a start date and it instantly shows how many days since then. It also auto-calculates milestones like 100 days, 200 days, 365 days, 1000 days, and so on.
There's more on top of that.
Date Calculator — Add or subtract any number of days from a given date, calculate the exact number of days between two dates, and see weekends and holidays marked.
Age Calculator — Enter your birthdate and it calculates your exact age, plus how many days until your next birthday. Supports Korean age too.
Anniversary Table — View everything from 10 days to 30,000 days at a glance. Date, day of the week, how many days from today, whether it's a holiday — all there.
Multilingual support too: Korean, English, Japanese, Chinese.
What I Learned Building It
Date calculations with JavaScript's Date object weren't that hard, but I started to understand why existing calculators mess up year counts. Edge cases are sneakily tricky.
I put some effort into the design. Since everything else looked so dated, I figured a modern look alone would be a differentiator.
Where Things Honestly Stand
I want to add more anniversary types like birthdays, wedding anniversaries, and work start dates, and I'd love to add reminders. But honestly, with utility tools like this, you build them and just wait for people to find them. No idea if traffic will come, but at least it's out there.
Want to try it? Check out the Anniversary Calculator.