Cultural Preservation
Tibetan Calendar
བོད་ཀྱི་ལོ་ཐོ།
A living astronomical tradition spanning over a millennium. Explore the lunisolar calendar rooted in the Kālacakra Tantra—tracking the Moon's phases and Sun's journey through ancient, sophisticated calculations.
The Idea
Far more than a system for marking days—a sophisticated astronomical and astrological framework that has guided Tibetan spiritual life for over a thousand years.
About
The Tibetan Calendar is a lunisolar system rooted in the Kālacakra Tantra—a text believed to have been taught by the Buddha himself. It tracks both the Moon's monthly phases and the Sun's annual journey, creating a framework that synchronizes celestial movements with spiritual practice.
Created by Thupten Chakrishar, this web application makes traditional Tibetan astronomical calculations accessible to anyone with a browser. The mathematical engine is based on Edward Henning's TCG (Tibetan Calendar Generator), implementing grub rtsis (siddhānta calculations) as described in classical texts. His scholarly work and open-source code made this digital adaptation possible.
☸ Date Calculator
Convert any date and discover its complete Tibetan astronomical properties:
- • Lunar Day (tshes) — The tithi or lunar date within the Tibetan month
- • Lunar Mansion (rgyu skar) — One of 27 star constellations the Moon passes through
- • Yoga (sbyor ba) — A combination of Sun and Moon positions creating 27 qualities
- • Karana (byed pa) — Half of a lunar day, with 11 types repeating through the month
Five Calculation Traditions
The software supports five distinct calculation systems, each with different epoch dates and parameters—a reminder that even within the tradition, "correctness" is not singular:
ཕུག་པ་ Phugpa
The most widely used, standardized in the "White Beryl" (1687)
མཚུར་ཕུ་ Tsurphu
Used by the Karma Kagyu school
འཁྲུལ་སེལ་ Error Correction
A refined system addressing accumulated drift
མཁས་པའི་སྙིང་ནོར།
An 18th-century scholarly tradition (Epoch: 1796 CE)
དགེ་ལྡན་རྩིས་གསར། New Ganden
Modern Gelug refinements (Epoch: 1747 CE)
Features
Date Calculator
Convert between Western and Tibetan dates with full astronomical properties
Monthly Calendar
Visual calendar display with Tibetan dates and lunar phases
Learning Resources
Comprehensive guides on months, years, days, time, and astrology
Tibetan Astrology
Element compatibility, animals, trigrams, and mewa calculations
Technical Details
Deep dive into the mathematics and algorithms behind the calculations
Lunar Phases
New moon, full moon, and practice days for Buddhist observances
Two Kinds of Truth
The calendar is religiously authoritative, yet astronomically approximate.
For Tibetan Buddhists, the calendar determines when to observe Buddha's birth, enlightenment, and parinirvāṇa; auspicious dates for empowerments and retreats; and monthly practice days. From a modern astronomical perspective, it contains known approximations—but this isn't a flaw. The calendar synchronizes a global community of practitioners, and its value lies in shared use, not astronomical perfection.
Why It Matters
- — Cultural preservation — Making a millennium-old astronomical tradition accessible in the digital age
- — Serving the diaspora — Helping Tibetans worldwide connect with their cultural heritage
- — Educational resource — Comprehensive learning materials for scholars and curious learners worldwide
- — Supporting practice — Enabling practitioners to observe auspicious days and festivals correctly
Technical & Attribution
Built with Astro and TypeScript. The core challenge was porting Edward Henning's C code, which uses custom BCD (Binary Coded Decimal) arithmetic for precision over millennia-spanning calculations.
Based on Edward Henning's TCG software and his seminal work "Kālacakra and the Tibetan Calendar" (Columbia University Press, 2007). Released under the MIT License.