A calendar date and a Vedic tithi are two different things. Your Gregorian calendar ticks over at midnight, every day the same 24 hours. A tithi doesn’t work that way. It can be shorter than a day or stretch beyond one, because it’s tied to the actual positions of the Sun and Moon in the sky, not to a clock.
How a tithi forms
A tithi is determined by the angular difference (longitude gap) between the Sun and the Moon. A new tithi begins every 12 degrees of that gap, giving 30 tithis across a lunar month. Since the Moon’s speed isn’t constant (it moves faster at some points in its orbit, slower at others), some tithis last 19 hours, others last 26. This is why you’ll sometimes see a tithi “skipped” on the calendar, or the same tithi listed on two consecutive days.
Here’s a concrete example. If Chaturthi starts at 4 AM on Monday and ends at 2 AM on Tuesday, it was active for 22 hours. But if the next tithi, Panchami, starts at 2 AM Tuesday and ends at 11 PM the same day, it lasted only 21 hours and the entire thing happened within a single calendar date. These variations aren’t errors; they’re just how lunar geometry works.
Shukla and Krishna Paksha
The first 15 tithis of the month are called Shukla Paksha (the waxing Moon), the next 15 are Krishna Paksha (the waning Moon). Purnima (full moon) and Amavasya (new moon) are the closing tithis of each half.
The character of each paksha matters for different activities. Shukla Paksha, with the Moon growing in brightness, is generally preferred for beginnings: starting a business, a wedding, grih pravesh, annaprashan. Krishna Paksha isn’t “bad,” but it’s considered more suitable for introspective work, completing ongoing tasks, and certain specific vratas and pujas tied to it (Shivratri, for instance, falls on Krishna Chaturdashi by definition).
The 30 tithis and their names
The count goes: Pratipada (1st), Dwitiya (2nd), Tritiya (3rd), Chaturthi (4th), Panchami (5th), Shashthi (6th), Saptami (7th), Ashtami (8th), Navami (9th), Dashami (10th), Ekadashi (11th), Dwadashi (12th), Trayodashi (13th), Chaturdashi (14th), and then either Purnima or Amavasya as the 15th. Certain tithis carry strong associations: Ekadashi for Vishnu fasting, Chaturthi for Ganesh, Ashtami and Chaturdashi for Devi and Shiva worship.
Why tithi matters for auspicious work
Some tithis are considered better suited to auspicious activities. For a wedding or a housewarming, tithi is usually the first thing checked in the panchang. A pandit looking at muhurat will typically start with the tithi, then check the nakshatra, then yoga and karana. Tithi is layer one.
This is also why you can’t just pick a “good date” from a generic list printed for all of India. The tithi prevailing at a specific hour in your city depends on the Moon’s exact position relative to the Sun, and that changes by the minute.
Check today’s tithi
Use the panchang tool to see today’s tithi, including its paksha, calculated for your specific location.