Rahu Kaal Explained: How It Is Calculated and How People Use It

Rahu Kaal (also written Rahu Kalam or Rahukalam) is a period of about an hour and a half every day that is traditionally considered unsuitable for starting something new — signing an agreement, beginning a journey, buying an important item or launching a business. Rahu is one of the two lunar nodes in Vedic astrology, treated as a shadowy planet, and the period is named after it.

Ongoing routines, daily work and prayer are generally not affected. The guidance is about beginnings, not about ordinary activity.

The time between local sunrise and local sunset is divided into eight equal parts. Rahu Kaal is one of those eight parts, and which one depends on the weekday. The order is the same everywhere:

• Monday — 2nd part
• Tuesday — 7th part
• Wednesday — 5th part
• Thursday — 6th part
• Friday — 4th part
• Saturday — 3rd part
• Sunday — 8th part

Suppose sunrise is at 6:00 a.m. and sunset at 6:00 p.m. — a 12-hour day. Each of the eight parts is 90 minutes. On a Monday the second part runs from 7:30 to 9:00 a.m. On a Saturday the third part runs from 9:00 to 10:30 a.m. On a Sunday the eighth part is the last one, 4:30 to 6:00 p.m.

In real life the day is rarely exactly 12 hours, so each part is a little longer or shorter. In winter in northern India the parts are closer to 80 minutes; in summer, closer to 100.

Because the calculation starts from local sunrise and sunset, Rahu Kaal in Chennai on a given Monday is not at the same clock time as in Delhi. It also drifts across the year as day length changes. This is why a fixed table printed as "Monday 7:30–9:00" is only an approximation, and why a tool that uses your city's actual sunrise is more reliable.

A few printed almanacs simplify by assuming a fixed 6 a.m. to 6 p.m. day. This is a convention rather than an astronomical calculation, and can differ from a sunrise-based method by several minutes.

Two similar windows are calculated the same way — dividing the daytime into eight parts and picking one by weekday — but using different weekday tables. Gulika Kaal (linked to Saturn's son Gulika) is generally regarded as a period during which whatever begins tends to repeat, which is why it is avoided for auspicious starts but not for tasks one wants to repeat. Yamaganda is another period regarded as unfavourable for beginning important work. Traditions differ on how strictly to treat each.

Rahu Kaal is a traditional timing aid, not a scientific prediction. Regional practice varies: it is followed very closely in much of South India and is often checked before travel or business decisions in the rest of the country. If an event has to happen at a fixed time — an exam, a flight, a wedding — most people simply proceed. Treat it as one input among several, alongside the tithi, nakshatra and Choghadiya.