Guide
Why Rahu Kaal Changes Every Day (The Real Reason)
Short answer: Rahu Kaal is not a clock time, it is a fraction of daylight. It is calculated by taking the exact time from sunrise to sunset on a given day, in a given place, and dividing it into eight equal parts. One of those eight parts, chosen by the weekday, is Rahu Kaal. Because the length of daylight itself changes every single day (and is different in every city), the clock time of Rahu Kaal has to change too. A table that says "Rahu Kaal is always 4:30 PM to 6 PM on Sunday" is, at best, a rough approximation for one specific city on one specific date of the year.
The part almost nobody explains: why daylight length changes at all
Earth's axis is tilted about 23.4° relative to its orbit around the Sun. That tilt is the entire reason seasons exist, and it is also the reason the number of daylight hours is different in June than in December, and different again in September. Near the equator the change is small; the further a city is from the equator, the bigger the swing. Delhi's longest day (around the June solstice) is roughly 14 hours; its shortest (around the December solstice) is roughly 10 hours 20 minutes. That is nearly four hours of difference across the year, in the same city.
Since Rahu Kaal is always exactly one-eighth of that daylight span, a four-hour swing in day length becomes roughly a 30-minute swing in how long the Rahu Kaal window itself lasts (about 105 minutes near the summer solstice versus about 78 minutes near the winter one), on top of the window also sliding earlier or later in the day as sunrise and sunset themselves shift.
Why the same weekday differs city to city
Sunrise and sunset are local solar events, tied to a place's longitude and latitude, not to its time zone. Two cities in the same time zone can have noticeably different sunrise times if they sit at different longitudes: local solar time shifts by about 4 minutes for every degree of longitude, and Kolkata sits about 11° east of Delhi, so its sunrise falls roughly 40-45 minutes earlier, even though both cities use the same IST clock. So the same weekday, the same "period 5 of 8" rule, still lands at a different clock time in each city, simply because each city's own sunrise is different.
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Where the eight-part system and the weekday rule actually come from
This method belongs to a broader system of Kaal Vibhajan (time-division) used in Hindu Panchang calculation, which treats the daylight period as the base unit for several classifications, not just Rahu Kaal. Yamaganda and Gulika Kaal use the same eight-part division of the same daylight span, just with their own separate weekday-to-period assignment, which is why the three practically never overlap. All three are computed the identical way once you have one number: the true local sunrise and sunset for that day.
Why so many published tables are wrong, or only roughly right
Most Rahu Kaal calendars and phone widgets you'll find either (a) hard-code one city's figures and apply them nationally, or (b) recompute sunrise and sunset only occasionally rather than for the exact requested date. Both shortcuts are invisible on any single day, because the error is usually only a few minutes, but they compound across the year: a table built from a spring sunrise time will be increasingly wrong by the time summer or winter arrives. The only way to get it right every day is to compute real sunrise and sunset for that specific date and that specific city each time, which is what the calculator on this site actually does, rather than reading from a stored table.
Frequently asked questions
Is Rahu Kaal the same time every Tuesday?
No. It moves earlier or later through the year as sunrise and sunset shift, and it is a different length in summer than in winter, because it is always exactly one-eighth of that day's actual daylight.
Why is my city's Rahu Kaal different from a table I found online?
Most likely the table was built for a different city, or for a different date than today, or hard-coded from one calculation done months ago. Sunrise and sunset need to be recalculated for your exact city and exact date.
Do Rahu Kaal, Yamaganda and Gulika Kaal ever overlap?
Rarely, because each follows its own separate weekday-to-period rule across the same eight daylight segments, so they are usually different windows on the same day.
Does Rahu Kaal apply at night too?
The classical calculation is for daylight (sunrise to sunset). Night has its own eight-part division for other purposes, but Rahu Kaal itself is a daytime concept.
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