Thiruvalluvar Calendar was created by Arivumani Velmurugan to bring the Tamil culture into the world. Currently Sidereal based calendars are used as Tamil Calendar. This calendar not aligns with Current Gregorian Calendar which is used in worldwide. It does not have fixed leap year system and fixed number of days per month.

This calendar is based on Thiruvalluvar Era (31 BCE). Currently Tamilnadu (India) Government has following Thiruvalluvar based Tamil Sidereal calendar system. In this calendar, 13 months are introduced instead of conventional 12 month system. 365 days are equally distributed in 12 months except first month. So first month is designed as leap month which has 29 days in normal year and 30 days in leap year. 

In 400 year cycles, 4800 (12x400) months out of 5200 (13x400) are equal unique months of 28 days (92.3%). 303 months out of 5200 has 29 day months (5.8274%). 97 months out of 5200 has 30 day months (1.87%).

New Year Day

The calendar always starts on January 15 every year (Approximate date for Thiruvalluvar Day). Gregorian New year also falls on 13th month of 15th day in Tamil Calendar. Tamil cultural festivals are most concentrated in the month of 'Thai'. So the calendar is made to start on Thai 1 / January 15.

Calendar Structure
No Month name Gregorian start date Days per month
1 Paamathi (பாமதி) Jan 15 29/30*
2 Ilmathi (இல்மதி) Feb 13/14* 28
3 Thuramathi (துறமதி) Mar 13 28
4 Uzhmathi (ஊழ்மதி) Apr 10 28
5 Arasumathi (அரசுமதி) May 8 28
6 Amaichumathi (அமைச்சுமதி) Jun 5 28
7 Aranmathi (அரண்மதி) Jul 3 28
8 Koozhmathi (கூழ்மதி) Jul 31 28
9 Padaimathi (படைமதி) Aug 28 28
10 Natpumathi (நட்புமதி) Sep 25 28
11 Kudimathi (குடிமதி) Oct 23 28
12 Kalamathi (களமதி) Nov 20 28
13 Karpumathi (கற்புமதி) Dec 18 28
Total 365/366*
  • - In leap years.


There are various type of months used in calendars. Mainly Synodic months are used in most of calendars (29/30 days=Average of 29.53058). In solar calendars, 30 day months and 31 day months are used. No calendar shows sidereal month, tropical month, anomalistic month and draconic month. These months are having 27+x days. So 28 day month approximates these type of months. So it is approximately relates to sidereal.

Day and Week

Most of the calendars in the world uses the week of 7 day cycle. This week cycle is uninterrupted. Year of 365 and 366 days are not fit entirely into the week cycle. Two additional weekdays (Days out of week cycle) are assigned to additional days.

Weekday names are derived from Thirukkural Chapters starting with vowels.






Aranthinam (அறந்தினம்)





Aalvinam (ஆள்வினம்)





Idanthinam (இடந்தினம்





Eegaithinam (ஈகைதினம்)





Uzhavinam (உழவினம்)





Ukinam (ஊக்கினம்)





Otrinam (ஒற்றினம்)





Thasathi (தசதி்)

Thamizh Sarvadesa Thinam means International Tamil Day

தமிழ் சர்வதேச தினம்

Once in a Year

Paamathi 29

Netti (நெட்டி) [Leap Day - Day in a Leap Year]

நெட்டாண்டில்  மட்டுமே வரும் சிறப்பு தினம்

Once in a Leap Year

Paamathi 30

In this calendar, All dates are permanently fixed with weekdays. Every Year, Every Month and Every week starts with Aranthinam and ends with otrinam (Except First Month).


  1. The calendar has two type of months. One type is Normal Months (2-13) have 28 days each (Exactly 4 weeks). Another type of month is Leap month i.e., First month. First month is larger than other months dedicated to God.
  2. Month names are derived directly from 13 episodes of Thirukkural.
  3. Starting Weekday in the all months are same. The same structure because of 4 weeks (28 Days).
  4. Day to Day calculation, Weekday finding methods are so easy compared to Current Civil Calendar.
  5. 13 months is very special for us. In Tamil letters includes 12 vowels and 1 ayutha letter. Tamil calendar (Thasathi) includes 12 months of 28 days and one month of 29 or 30 days.
  6. Total Tamil letters are 247=13x19. 2+4+7=13. So 13 is the best Tamil number. This number is unlucky for some countries.
  7. 28 division clock is enough to show 28 days, 14 month divisions (13 months of 28 days +Additional Leap days), and 7 weekdays. 28:14:7 = 4:2:1
  8. We will celebrate Thiruvalluvar Day, Thirukkural Day as a Part of World Tamil Day or Tamil International Day on Paa 29 which is equal to February 12. Separate International day for Tamil people.
  9. We will celebrate the Leap Day as Netti in Paa 30 which is equal to February 13 in Leap year.
  10. Year is divided into 4 quarters.
    1. First Quarter: Paa(1) 1 - Uzh(4) 6 = 91/92 Days (Paavoozh)
    2. Second Quarter Uzh(4) 7 - Aran(7) 13 = 91 Days (Uzharan)
    3. Third Quarter Aran(7) 14 - Natpu(10) 20 = 91 Days (Natparan)
    4. Fourth Quarter Natpu(10) 21 - Karpu(13) 28 = 92 Days (Natkarpu)
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