A calendar date and a Vedic tithi are two different things.
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.
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.
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.
Check today’s tithi
Use the panchang tool to see today’s tithi, including its paksha, instantly.
This information is descriptive.