Whatistheday – Day of the Week Calculator
Whatistheday is a free weekday calculator and multi-calendar date converter. Find the exact day of the week for any date — past, present, or future — with 100% mathematical accuracy.
Features
- Weekday Calculator: Instantly determine what day of the week any date falls on, from 4000 BC to thousands of years in the future.
- 10+ Calendar Systems: Convert dates across Gregorian, Hebrew, Islamic (Hijri), Julian, Chinese Lunar, Hindu (Vikram Samvat), Maya (Long Count), Egyptian, and Babylonian calendars.
- BC/BCE Support: Full support for ancient and historical dates using the Proleptic Gregorian and Julian calendar systems with astronomical year numbering.
- Date Calculators: Business days calculator, age calculator, date difference, day of year, ISO week number, and leap year checker.
- 50+ Country Holidays: View public holidays and countdowns for over 50 countries worldwide.
Accuracy
Our engine uses the Proleptic Gregorian Calendar for modern and future dates and the Julian Calendar for dates before the Gregorian Reform of 1582. This dual-system approach ensures historically accurate weekday results for any era, making it ideal for academic research, genealogy, and religious calendar synchronization.
Whatistheday is completely free, requires no registration, and works on any device. All calculations are performed locally in your browser for instant results and total privacy.