---
type: Concept
bundle: jyotisha-kala
bundle_version: 0.12.0
id: tithi
title: Tithi
iast: Tithi
devanagari: तिथि
description: 'The lunar day: the time in which the Moon gains twelve degrees of elongation on the Sun, thirty to a synodic month; NOT a solar day, NOT a calendar date, NOT a fixed length of time.'
darshana:
- Jyotiṣa
text_source: Sūrya Siddhānta 2; Vedāṅga Jyotiṣa
tags:
- tithi
- lunar-day
- panchanga
- calendrics
- jyotisha
not:
- term: 'a solar day'
  why: 'A tithi is defined by relative motion, not by sunrise: it runs from about 19 to about 26 hours as the Moon’s speed varies. A tithi wholly contained between two sunrises drops from the civil count (kṣaya); one spanning two sunrises repeats (vṛddhi). Mapping tithi to “day” breaks every observance calculation built on it.'
  instead: 'Render tithi as lunar day with the elongation definition stated, and keep the Sanskrit term.'
- term: 'a calendar date'
  why: 'Dates are civil conventions; the tithi is an astronomical quantity that begins and ends at computable instants. The almanac’s job is exactly to say which tithi is current at which civil time.'
- term: 'a fixed length of time'
  why: 'Thirty tithis per synodic month makes the MEAN tithi about 23.6 hours, but no actual tithi need have that length. The unit is angular (12° of elongation), not temporal.'
related:
- /concepts/masa.md
- /concepts/karana.md
- /concepts/panchanga.md
timestamp: '2026-07-09'
okf_version: '0.2'
license: CC BY-SA 4.0
---

# Tithi -- तिथि

**Not:** a solar day, a calendar date, a fixed length of time

## What It Actually Means

A tithi is the time in which the Moon gains twelve degrees of elongation on the Sun. Thirty make a synodic month: fifteen bright (śukla-pakṣa), new moon to full, fifteen dark (kṛṣṇa-pakṣa). Because lunar speed varies, tithis stretch and shrink, producing the kṣaya and vṛddhi phenomena that make Hindu calendrics genuinely technical. The Vedāṅga Jyotiṣa already counts 1,860 tithis in its five-year yuga, and virtually the whole ritual calendar, ekādaśī fasts, festival days, śrāddha timing, is keyed to tithi rather than to solar date.

## Audience Metaphor

A lap measured by distance gained, not by the stopwatch: the runner (Moon) completes a tithi when it has gained a fixed lead over the pacer (Sun), however long that takes. Some laps are fast, some slow; the count of laps, not the clock, is what the ritual calendar reads.

## Citations

1. Vedāṅga Jyotiṣa on the five-year yuga of 1,860 tithis -- see [references/lagadha-vedanga-jyotisha.md](../references/lagadha-vedanga-jyotisha.md)
2. Sūrya Siddhānta 2 on tithi from elongation -- see [references/surya-siddhanta.md](../references/surya-siddhanta.md)
