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How is Rahu Kalam Calculated?
Step-by-Step Formula, Weekday Table, and Today's Timing
What is Rahu Kalam?
Rahu Kalam (ராகுகாலம்) is a daily inauspicious period of approximately 90 minutes, believed to be governed by Rahu — the north node of the Moon in Vedic astrology. Rahu is associated with sudden changes, karmic challenges, and the unpredictable. Traditional Tamil practice avoids starting any new auspicious activity during this window.
Unlike some other Panchangam elements, Rahu Kalam is not derived from planetary longitudes. It is a fixed formula based solely on the day of the week and the local sunrise/sunset times.
The Calculation Formula
- Find sunrise and sunset for the day and location.
- Calculate day duration = Sunset time − Sunrise time (in minutes).
- Divide by 8 to get one octave = day duration ÷ 8.
- Find the Rahu octave using the weekday table (Sunday=8, Monday=2, etc.).
- Compute Rahu Kalam start = Sunrise + (octave × (Rahu octave number − 1)).
- Compute Rahu Kalam end = Rahu Kalam start + one octave duration.
Example: On a Monday in Chennai with Sunrise at 6:05 AM and Sunset at 6:20 PM:
Day duration = 735 minutes. One octave = 735 ÷ 8 ≈ 91.9 minutes.
Monday = octave 2. Rahu Kalam start = 6:05 AM + (91.9 × 1) = 7:37 AM.
Rahu Kalam end = 7:37 AM + 91.9 min ≈ 9:09 AM.
Weekday Table
Each day of the week carries its own ruling planet and significance in Vedic astrology. In Panchangam, the weekday is called Vara — learn more about how Vara is defined and which planets rule each day.
| Day | Octave # | Position in Day | Approximate Time (6 AM sunrise) |
|---|---|---|---|
| Sunday | 8/8 | Octave 8 of 8 | 7:30 PM – 9:00 PM (approx, 6 AM sunrise) |
| Monday | 2/8 | Octave 2 of 8 | 7:30 AM – 9:00 AM (approx) |
| Tuesday | 7/8 | Octave 7 of 8 | 3:00 PM – 4:30 PM (approx) |
| Wednesday | 5/8 | Octave 5 of 8 | 12:00 PM – 1:30 PM (approx) |
| Thursday | 6/8 | Octave 6 of 8 | 1:30 PM – 3:00 PM (approx) |
| Friday ★ | 4/8 | Octave 4 of 8 | 10:30 AM – 12:00 PM (approx) |
| Saturday | 3/8 | Octave 3 of 8 | 9:00 AM – 10:30 AM (approx) |
★ = today (Friday). Approximate times assume 6:00 AM sunrise. Actual times vary by location and season.
Frequently Asked Questions
How is Rahu Kalam calculated?
Rahu Kalam is calculated by dividing the duration between sunrise and sunset into 8 equal parts. The specific part depends on the day of the week: Sunday=8th, Monday=2nd, Tuesday=7th, Wednesday=5th, Thursday=6th, Friday=4th, Saturday=3rd.
Does Rahu Kalam change every day?
Yes. Because sunrise and sunset times change daily (and vary by location), the exact clock time of Rahu Kalam shifts each day. The day-of-week formula remains constant, but the window's start and end times are always computed from that day's sunrise and sunset.
Is Rahu Kalam the same across India?
No. Rahu Kalam is location-dependent. Because sunrise varies by latitude and longitude, the Rahu Kalam window at Chennai is different from that at Mumbai, Delhi, or London on the same day.
What should be avoided during Rahu Kalam?
It is traditionally advised to avoid starting new ventures — business meetings, travel, signing contracts, auspicious ceremonies, or any new beginning — during Rahu Kalam. Routine activities already in progress are generally considered unaffected.