What Rahu kaal is, and what it is not

Rahu kaal is one eighth of the daylight. Take the time from sunrise to sunset at your own place, cut it into eight equal parts, and one of those parts belongs to Rahu. Which part depends only on the weekday, by a rota that never changes.

It is not a fixed clock time. It is not the same length all year, and it is not the same in two towns on the same morning. It follows your sunrise and your sunset, so it stretches in summer and shrinks in winter.

Traditionally it is avoided for starting something new that could as easily start an hour later. It has never been a rule about what is already running, about what you do not choose, or about an emergency.

Rahu kaal takes the 8th part of the daylight on Sunday, the 2nd on Monday, the 7th on Tuesday, the 5th on Wednesday, the 6th on Thursday, the 4th on Friday and the 3rd on Saturday. Nothing about the sky enters that list. It is a fixed assignment, carried in an almanac rhyme and memorised.

On a nominal day of sunrise at six and sunset at six, each eighth is an hour and a half, which puts Monday’s Rahu kaal at 07:30 to 09:00 and Sunday’s at 16:30 to 18:00. Those are the times most people half-remember. Real sunrises are not at six, so the real windows are not on the half hour.

Because a part is an eighth of the actual daylight, its length is a measurement rather than a constant. At Chennai this engine puts the daylight at 12 hours 54 minutes on 21 June 2026 and 11 hours 21 minutes on 21 December, so Rahu kaal runs about 97 minutes in late June and about 85 in late December. Further north the swing is wider: at Delhi the same two days give about 105 minutes and about 77.

It moves with the place as well as the season. Sunrise runs about four minutes later for every degree of longitude westward, so an almanac printed for one town is minutes out for another, and the whole window slides with it.

That is the usual reason a printed Rahu kaal disagrees with the one on this page. It is rarely a difference of tradition. It is a difference of address.

The rule is about beginnings, and about beginnings you are choosing the hour of. Households avoid setting out on a journey in the window, making a purchase, signing a paper, paying a first instalment, opening a shop, making a first visit to a family, or taking the first step of a piece of work that has no particular reason to start now.

The test a household actually applies is two questions. Is this a beginning? Can it wait an hour? If both answers are yes, it waits.

Where a proper hour is wanted and nothing is free, the standing fallback is Abhijit, the auspicious muhurtam around noon. Almanacs do not count it on a Wednesday.

It has never meant that something already under way must stop. A journey that began before the window continues through it. Work in progress continues. Nobody puts down a lesson, a meal or a piece of machinery because an eighth of the day has come round.

It has never applied to what is not chosen. The school day, the office, a train that leaves when it leaves, a hearing listed for a time, a shift that starts when the shift starts. None of these is a beginning whose hour is yours to move.

And it has never applied to an emergency. Going to a hospital, calling for help, dealing with a fire or a flood: the tradition does not ask anyone to wait, and nothing on this site should be read as asking it. The observance is a preference about optional beginnings. It is not a prohibition on living, and treating it as one is a misreading of it rather than a stricter form of it.

Two more eighths are picked the same way and avoided for beginnings in the same spirit. Yamaganda takes the 5th part on Sunday, then the 4th, 3rd, 2nd and 1st through Thursday, the 7th on Friday and the 6th on Saturday. Gulika, the part of Sani’s son, has the simplest rota of the three: the 7th part on Sunday, one part earlier each day, the 1st on Saturday.

The three never overlap on the same day, which is why an ordinary weekday loses three eighths of its daylight to them and no more.

Nalla neram, the good window a Tamil almanac prints twice a day, is chosen out of the Gowri parts that touch none of the three, so it never collides with them. The muhurtham search does the same thing at greater length: it walks the rising sign through the daylight and then cuts these three windows out of what it found.

The eighths are exact. Sunrise and sunset here are within 1.7 seconds of the Swiss Ephemeris on the same convention, so the edges of the window are as well determined as the day itself is.

Which eighth belongs to Rahu is a rule, and the rule is all there is. No measurement produces it, and none could. That the hour is unfavourable is a belief the tradition holds; this site computes the window exactly as the tradition defines it and takes no position on what it means.

That is worth stating plainly, because a panchangam prints a sunrise and a Rahu kaal one under the other in the same type, and they are not the same kind of claim. The sunrise you can check against the horizon. The window is arithmetic on a definition, correct as arithmetic, and silent about the sky between half past one and three.

The five limbs of a day, with the good and bad hours.

Panchangam →