To calculate Rahu kaalam, the day duration from Sunrise to Sunset, at a particular location is divided into eight equal parts. There is no Rahu Kaalam during the first period of any weekday. On Sunday it falls on 8th period, Monday 2nd period, Saturday 3rd period, Friday 4th period, Wednesday 5th period, Thursday 6th period and Tuesday 7th period. Rahu kaalam and Yama Ghandam are the two time periods which are especially considered inauspicious for any new undertakings.

Rahu Kaalam Calculation :

Example : Sunrise 6:00 a.m. Sunset 6:00 p.m. 1/8 of Day = 90 minutes

Rahukaalam (also spelled as Rahukal or Rahu kalam) or the period of Rahu is a certain amount of time every day that is considered inauspicious for any new venture according to Indian astrology (Vedic). In Hindu mythology, Rahu Kala is one of the 8 segments of the day and considered inauspicious period in Indian astrology due to its associated with malefic, Rahu . The segments are calculated by taking the total time between sunrise and sunset, at a given place, and then dividing this time duration by 8. Astronomically in the Hindu Panchangas, the ever varying planetary configurations mean that the auspicious hours during each day will not always fall at the same moment of time. Rahukalam and Yama Ghantam are the two time periods which are especially considered inauspicious or unlucky (Ashub).

The planets according to Indian astronomers were the Sun, Moon, Mars, Mercury, Venus, Jupiter,Saturn, Rahu and Ketu. Rahukaalam and Gulikaalalam are calculated based on these planets. Even though Rahu and Ketu are not physical bodies, they are sensitive points on the intersection of theecliptic (the apparent path of motion of the Sun) by the Moon's orbit. Rahu is the northern point and Ketu is the southern point. Ancient astronomers felt that the mighty Rahu and Kethu have the strength to eat the sun, thus causing a solar eclipse. Hence it is considered inauspicious to begin any undertaking during this "Rahukaalam". Every day this Rahukaalam lasts for around 90 minutes, but the duration differs according to the length of the time between sunrise to sunset. To calculate Rahukaalam, the time between the sunrise and sunset is divided into 8 units or time-groups, which time-group will have the Rahukaalam depends on the weekday.

The Rahu Kalam is very important in Southern Part's of India. It Varies from Place to Place, changing every day it is based on Sunrise ans Sunset at your place.

1/8th part of each day is termed as the Rahu Kalam(The period of the north node). This part of the day is most inauspicious and should be avoided for all important activities. Do not sign any major documents or start a new enterprise in this period. This period will vary with different latitudes by a few minutes. The table below gives the broad time range of this period. This will be applicable to all places.