Vedic Tithi & Lunar Day Calculator

What is a Tithi? The Sacred Science of Vedic Lunar Days

In Vedic astrology (Jyotish), time measurement relies on both solar and lunar rhythms. While a solar day is defined by Earth's 24-hour rotation on its axis, a Tithi is an astronomical lunar day defined by orbital geometry. Specifically, a Tithi represents the precise period during which the longitudinal separation between the Moon (Chandra) and the Sun (Surya) increases by exactly 12 degrees.

Because the Moon's elliptical orbit causes its apparent velocity to speed up near perigee and slow down near apogee, the duration of a Tithi varies continuously between 19 and 26 solar hours. A full lunar synodic cycle spans 360 degrees of longitudinal separation, which yields exactly 30 Tithis per lunar month. These 30 lunar days are divided into two equal fortnights: Shukla Paksha (the waxing fortnight) and Krishna Paksha (the waning fortnight).

Astronomical Computation: Calculating Lunar Elongation and the 12 Degree Arc

The exact calculation of a Vedic Tithi is governed by the mathematical difference between lunar and solar ecliptic longitudes. In traditional Sanskrit terminology, this elongation is derived using the formula:

Tithi Index = Floor[(Chandra Sphuta - Surya Sphuta) / 12°] + 1

When both the Sun and the Moon occupy the exact same celestial degree (0 degrees separation), the phase is Amavasya (New Moon). As the Moon advances eastward relative to the Sun, each 12-degree arc initiates a new Tithi. When the separation reaches 180 degrees, the phase culminates at Purnima (Full Moon). AstroLeaf computes these positions using high-precision Swiss Ephemeris algorithms, ensuring accurate start and end timestamps down to the second.

Complete 30-Tithi Master Reference Matrix

Every lunar month contains 30 Tithis categorized by Category (Shreni), Element (Tattva), Ruling Deity, Planetary Lord, and Muhurat recommendations:

Shukla Paksha vs Krishna Paksha: Light, Mind, and Momentum

The lunar month is split into two distinct cosmic phases that deeply influence human psychology and external energy. Shukla Paksha, known as the bright fortnight, begins immediately after Amavasya and continues until the Full Moon. As lunar illumination expands, solar reflection increases. In Vedic philosophy, Shukla Paksha represents upward growth, optimism, outward manifestation, and constructive vitality. It is universally favored for weddings, real estate purchases, new investments, and commercial ventures.

Krishna Paksha, known as the dark fortnight, begins immediately after Purnima and continues until the New Moon. As the Moon gradually wanes, lunar illumination diminishes. Krishna Paksha represents inward contemplation, introspection, analytical review, spiritual purification, and the release of unwanted habits. While major celebrations are generally scheduled during Shukla Paksha, Krishna Paksha provides deep spiritual focus for meditation, research, debt clearance, and ancestral gratitude.

The Five Tithi Shrenis: Nanda, Bhadra, Jaya, Rikta, and Poorna

Classical Vedic texts such as Muhurta Chintamani and Brihat Samhita organize the 15 lunar days into five functional categories known as Shrenis. Each category embodies a distinct cosmic element (Pancha Mahabhuta) that sets the tone for specific actions:

• Nanda (Joyous, Earth Element): Includes the 1st, 6th, and 11th Tithis. These days promote prosperity, happiness, and celebrations. They are ideal for planting seeds, laying foundations, and starting education. Avoid borrowing debt.
• Bhadra (Auspicious, Water Element): Includes the 2nd, 7th, and 12th Tithis. These days provide enduring stability. They are suitable for weddings, house construction, vehicle purchases, and long-term contracts. Avoid harsh legal litigation.
• Jaya (Victorious, Fire Element): Includes the 3rd, 8th, and 13th Tithis. These days generate courage and breakthrough momentum. They support sports, competitive examinations, legal strategy, and mechanical work. Avoid destructive squabbles.
• Rikta (Cleansing, Air Element): Includes the 4th, 9th, and 14th Tithis. Rikta literally means empty or clearing. These days are reserved for detoxing, obstacle removal, spiritual fasting, and Ganesha worship. Major commercial and celebratory launches are strictly avoided.
• Poorna (Complete, Ether Element): Includes the 5th, 10th, 15th, and 30th Tithis. Poorna means fulfillment. These days are optimal for major religious ceremonies, family feasts, fasting vows, and peaceful social gatherings. Avoid anger and unprincipled trade.

The Udaya Tithi Principle in Vedic Panchang and Festivals

A common question in Hindu timekeeping is why two people in different cities might celebrate a festival on different days, or why a festival continues throughout the day even if the Tithi changes by midday. The explanation lies in the principle of Udaya Tithi (Sunrise Tithi).

According to classical Panchang rules, the specific Tithi that is active at the exact moment of local sunrise becomes the governing Tithi for all religious rituals, fasts, and civic calendar dates for that entire solar day. For example, if Ekadashi begins 10 minutes before sunrise and ends at 4:00 PM, the entire civil day is treated as Ekadashi for fasting and temple worship. Conversely, if Ekadashi starts 10 minutes after sunrise, it is not the Udaya Tithi for that day, and the main Ekadashi fast will be observed on the subsequent sunrise day. Because sunrise times vary across global longitudes and latitudes, festival dates can shift by one calendar day between India, Europe, and the Americas.

Kshaya Tithi and Vriddhi Tithi: Skipped and Extended Lunar Days

Because the Moon moves in an elliptical path rather than a perfect circle, its speed across the sky is variable. This astronomical variation creates two phenomena known as Kshaya Tithi and Vriddhi Tithi:

• Kshaya Tithi (Skipped Tithi): When the Moon is near perigee, it moves rapidly. If a Tithi starts shortly after sunrise on Monday and concludes before sunrise on Tuesday, that Tithi does not touch any sunrise. As a result, it is skipped in the civic calendar. While its micro-hours remain accessible for personal meditation, classical astrology discourages scheduling permanent milestones like housewarming or marriage on Kshaya days.
• Vriddhi Tithi (Extended Tithi): When the Moon is near apogee, its orbital speed slows. If a Tithi starts just before sunrise on Wednesday and extends past sunrise on Thursday, it touches two consecutive sunrises. The Tithi is counted on both calendar days in the daily Panchang, and the second day is often utilized for concluding major religious fasts.

Location-Dependent Panchang: How Coordinates and Timezones Shape Daily Tithi

A planetary calculation that is valid for New Delhi cannot be applied directly to London, San Francisco, or Sydney without precise geographic adjustment. A Tithi is a universal astronomical instant in UTC, but its interaction with civil dates depends entirely on local solar coordinates:

• Local Sunrise Timings: Because Udaya Tithi depends on the moment the upper limb of the Sun appears on the local horizon, variations in latitude and longitude shift the exact sunrise time.
• Timezone Conversion: When a Tithi ends at 10:00 PM Indian Standard Time (UTC+5.5), the exact same moment corresponds to 4:30 PM in London (UTC+0) and 8:30 AM in Los Angeles (UTC-8).
• Chandra Rashi and Nakshatra Transitions: The Moon's ingress into a new zodiac sign or Nakshatra occurs simultaneously in universal time, but the local civil hour and sunrise relationship differ around the globe.

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