The Tamil calendar is a derivative of the old Hindu solar calendar and is based on the sidereal year (i.e. the time taken for one revolution of the Earth around the sun, or the mean time taken by the sun to return to the same position relative to the background of the fixed stars in the sky). In contrast, most other languages of India (Telugu, Hindi) use lunar calendars.

• The Twelve Months
• The Sixty-Year Cycle
• The Seven-Day Week

The Twelve Months

The Tamil new year usually falls in mid-April and the calendar consists of twelve months. Unlike the Gregorian calendar, the number of days in a given month can vary between years. Moreover, Tamil months may even have 32 days. For example, the month of Vaikasi had 32 days in 1996 and 31 days in 1998. Similarly, Aani had 31 days in 1996 and 32 days in 1998.

The following table shows when the first day of each month occurs:

No.	Tamil month	in English	Start date	1997	1998	1999	2000	2001	2002	2003	2004
10.		Thai	January	14*	14*	15*	14*	14*	14*	15*	15*
11.		Maasi	February	12	13	13	13	12	12	13	13
12.		Panguni	March	14	15	15	14	14	14	15	14
1.		Chiththirai	April	14+	14+	14+	13+	13+	13+	14+	13+
2.		Vaikasi	May	15	15	15	14	14	14	15	14
3.		Aani	June	15	15	15	15	14	15	15	15
4.		Aadi	July	17	17	17	16	16	16	17	16
5.		Aavani	August	17	17	18	16	17	17	18	17
6.		Purattasi	September	17	17	18	16	17	17	18	17
7.		Aippasi	October	17	18	18	17	17	17	18	17
8.		Karthikai	November	16	17	17	16	16	16	17	16
9.		Markazhi	December	16	16	16	15	15	16	16	16

The Sixty-Year Cycle

Each year in the Tamil calendar has a name. These names follow a 60-year cycle. (The number 60 represents five Jovian periods i.e. it takes Jupiter about 12 years to orbit the sun).

The following table lists the cycle of sixty year names:

No.	Name	in English	Year
1		Prabhava	1987--1988
2		Vibhava	1988--1989
3		Sukla	1989--1990
4		Pramodhudha	1990--1991
5		Prajorpati	1991--1992
6		Angirasa	1992--1993
7		Srimukha	1993--1994
8		Bhava	1994--1995
9		Yuva	1995--1996
10		Dhatu	1996--1997
11		Isvara	1997--1998
12		Vehudhanya	1998--1999
13		Pramathi	1999--2000
14		Vikrama	2000--2001
15		Vishu	2001--2002
16		Chitrabanu	2002--2003
17		Subanu	2003--2004
18		Tarana	2004--2005
19		Parthiba	2005--2006
20		Viya	2006--2007
21		Sarvajit	2007--2008
22		Sarvadhari	2008--2009
23		Virodhi	2009--2010
24		Viruti	2010--2011
25		Kara	2011--2012
26		Nandana	2012--2013
27		Vijaya	2013--2014
28		Jaya	2014--2015
29		Manmatha	2015--2016
30		Dhunmuki	2016--2017
31		Hevilambi	2017--2018
32		Vilambi	2018--2019
33		Vikari	2019--2020
34		Sarvari	2020--2021
35		Plava	2021--2022
36		Subakrit	2022--2023
37		Sobakrit	2023--2024
38		Krodhi	2024--2025
39		Visuvasuva	2025--2026
40		Parabhava	2026--2027
41		Plavanga	2027--2028
42		Kilaka	2028--2029
43		Saumya	2029--2030
44		Sadharana	2030--2031
45		Virodhikritu	2031--2032
46		Paridhabi	2032--2033
47		Pramadhisa	2033--2034
48		Ananda	2034--2035
49		Rakshasa	2035--2036
50		Nala	2036--2037
51		Pingala	2037--2038
52		Kalayukti	2038--2039
53		Siddharthi	2039--2040
54		Raudri	2040--2041
55		Dunmati	2041--2042
56		Dundubhi	2042--2043
57		Rudhrodhgari	2043--2044
58		Raktakshi	2044--2045
59		Krodhana	2045--2046
60		Akshaya	2046--2047

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The Seven-Day Week

The Tamil calendar also follows a seven-day week. The names of the seven days are analogous to those used in most other calendars i.e. they correspond to the same celestial bodies Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn, in that order.

The following table lists the days of the week in Tamil:

No.	Tamil day	in English	English day
1.		Nyaayitru-kizhamai	Sunday
2.		Thingat-kizhamai	Monday
3.		Sevvaai-kizhamai	Tuesday
4.		Budhan-kizhamai	Wednesday
5.		Vyaazha-kizhamai	Thursday
6.		Velli-kizhamai	Friday
7.		Sani-kizhamai	Saturday