Amrutkaal How Rahu Kaal Is Calculated
Rahu Kaal (राहु काल) is a traditional inauspicious window observed each day, and its calculation is purely arithmetical — there are no planetary positions involved. The rule is simple: take the length of daylight, from local sunrise to local sunset, and divide it into eight equal parts. Each weekday is assigned exactly one of these eight parts as its Rahu Kaal. Because the calculation depends only on sunrise and sunset, the duration of each part is roughly an eighth of the day — about 90 minutes when daylight is near twelve hours, but shorter in winter and longer in summer. This also means Rahu Kaal is never the same clock time for two different places: a city further east, or one at a different latitude, will see different sunrise and sunset, so its eight parts begin and end at different moments. Understanding the method matters because almost every Rahu Kaal table you encounter is generated by this single rule applied to one location's ephemeris. It is a calendrical convention from the muhurta tradition rather than a computation of where the shadow-point Rahu actually lies in the sky.
The Eight-Part Division
Begin with the interval between sunrise and sunset for your location and date — this is the daylight span. Divide that span into eight equal segments. If the day length is exactly twelve hours, each segment is one and a half hours; if daylight is shorter or longer, each segment scales accordingly. Crucially, the segments are measured from actual local sunrise, not from a fixed hour like 6:00 a.m.
Each weekday claims one segment as its Rahu Kaal. The traditional mapping is: Monday — the 2nd part; Saturday — the 3rd part; Friday — the 4th part; Wednesday — the 5th part; Thursday — the 6th part; Tuesday — the 7th part; Sunday — the 8th (last) part. Notice that the very first part, immediately after sunrise, is never Rahu Kaal on any day of the week.
A worked example makes this concrete. Suppose sunrise is 6:00 a.m. and sunset is 6:00 p.m., giving twelve hours of daylight and eight parts of 90 minutes each. On a Monday, Rahu Kaal is the 2nd part — 7:30 a.m. to 9:00 a.m. On a Sunday it is the 8th part — 4:30 p.m. to 6:00 p.m. Change the sunrise or sunset, and every boundary shifts proportionally.
Why It Varies by City
Sunrise and sunset are local astronomical events that depend on longitude, latitude, and the date. Two cities on the same day will generally have different sunrise and sunset times, so when each divides its own daylight into eight, the resulting part-boundaries differ. A Rahu Kaal table computed for Delhi is therefore not valid for Chennai or Mumbai — the weekday-to-part rule is identical, but the underlying day length and start time are not.
This is why a precise panchang always ties Rahu Kaal to a specific place. For an accurate window you should use the sunrise and sunset of your own city rather than a generic table. It is also worth restating that this is a traditional timekeeping rule, not a prediction derived from the live position of Rahu; the method is fixed and reproducible for any location whose sunrise and sunset are known.
Frequently Asked Questions
Is Rahu Kaal always ninety minutes long?
No. Each part is one-eighth of the daylight span, so it equals about 90 minutes only when day length is near twelve hours. In winter the parts are shorter and in summer they are longer, varying with the season and latitude.
Why is the first part of the day never Rahu Kaal?
The traditional weekday-to-part assignment simply does not use the 1st segment for any day — the earliest any weekday's Rahu Kaal can fall is the 2nd part, which is Monday's. It is a convention of the rule, not an astronomical result.
Can I use one Rahu Kaal table for the whole country?
No. Because the parts are measured from local sunrise to local sunset, the timings differ by city. A single national table will be wrong for most places; always use timings computed for your own location.