A few months ago I realized something every time I needed to know what week it was I had to Google it. The results were cluttered with ads and outdated information. So I decided to build weeknumber.cc —— a clean fast free week number calculator.
What does it do
It tells you the current week number. But it does a LOT more
- Date Week conversion —— Any date to week number any week number to dates
- Full year calendars —— 2015 through 2035 every year visualized
- 15 languages —— Chinese English Japanese Korean Spanish French German Portuguese Russian Arabic Hindi Thai Vietnamese Indonesian Turkish
- Free JSON API —— No API key CORS enabled
- Embeddable widget —— One line of HTML to add week numbers to any website
- Chrome Extension —— Quick popup in your browser
- Viral tools —— Birth week calculator countdown timer life-in-weeks visualizer comparison tool quiz
The Numbers
- 18000+ static HTML pages —— Every week of every year every date every month every language plus history pages
- 15 languages with proper hreflang tags
- 18623 URLs in the sitemap
- Zero frameworks —— Pure HTML/CSS/JS
- 0 hosting cost —— All on Cloudflare Pages free tier
The API my favorite part
Developers love this
bash
Get current week
curl https//www.weeknumber.cc/api/week
Get week for a date
curl https//www.weeknumber.cc/api/weekdate=2026-12-25
Get dates for a specific week
curl https//www.weeknumber.cc/api/weekyear=2026&week=1
Returns clean JSON
json
"week" 25
"year" 2026
"startdate" "2026-06-15"
"enddate" "2026-06-21"
"system" "ISO 8601"
No API key. No rate limits. Just works.
The Widget
Add this to any website
html
div class="wn-widget" data-lang="zh"/div
script src="https//www.weeknumber.cc/widget.js" async/script
That's it. It renders a beautiful week number badge in any of 15 languages.
How I built it
The entire site is static HTML. I use a build script that generates every page programmatically —— every week of every year every date conversion every language variant. The result 18000+ pages that load instantly from Cloudflare's global edge network.
The API runs on Cloudflare Pages Functions their edge function platform. The OG image generation and widget are also serverless edge functions.
Why it's working
- Programmatic SEO —— 18000+ pages each targeting specific long-tail keywords like "week 25 2026" "what week is June 15" "25 2026"
- Hreflang tags —— Every page properly signals language variants to search engines
- Structured data —— FAQ and BreadcrumbList schema on every page
- 100% Core Web Vitals —— Pure HTML zero JavaScript on main pages loads in milliseconds
- Free backlinks —— The API and widget naturally attract developer links
Try it
Visit weeknumber.cchttps//www.weeknumber.cc
The API widget and all tools are completely free. I'd love to hear your feedback