Start with sunrise and sunset
Rahu Kalam is a traditional time window found in many Hindu panchangas. Under the popular daylight-eighth method, first calculate sunrise and sunset at the chosen place. Divide the daylight interval by eight, then assign one of those eight portions according to the weekday. No planetary ephemeris or birth chart is required to assign Rahu Kalam; the astronomy is in the solar boundary times.
Drik Panchang's method article calls this the popular Yamardha one-eighth method and states that other Rahu Kalam methods are also used. The rule below is therefore the rule this calculator implements, not a claim that every text or regional calendar uses one identical approach.
Which eighth belongs to each weekday?
| Weekday | Daylight eighth | If sunrise 06:00, sunset 18:00 |
|---|---|---|
| Sunday | 8th | 16:30–18:00 |
| Monday | 2nd | 07:30–09:00 |
| Tuesday | 7th | 15:00–16:30 |
| Wednesday | 5th | 12:00–13:30 |
| Thursday | 6th | 13:30–15:00 |
| Friday | 4th | 10:30–12:00 |
| Saturday | 3rd | 09:00–10:30 |
The last column is only arithmetic for an exact twelve-hour daylight span. A longer summer day makes every eighth longer; a shorter winter day makes each eighth shorter. The weekday is the day beginning at the selected date's sunrise. We use the civil date's weekday to select that sunrise-day interval.
A worked Sunday example
Suppose sunrise is 06:00 and sunset is 18:00. Daylight lasts twelve hours, so one eighth lasts ninety minutes. Sunday receives the eighth part, after seven have elapsed: 06:00 + 10 hours 30 minutes = 16:30. That segment ends at sunset, 18:00. If sunset instead falls at 17:00, the daylight span and resulting Sunday window both change; copying 16:30–18:00 would be wrong.
Limits of a local clock result
The free calculator asks for latitude, longitude, a civil date, and one fixed UTC offset. It models sunrise and sunset using the site's bundled Astronomy Engine and a standard apparent-Sun/refraction convention at zero metres. The actual observed crossing can shift with elevation, an obstructed horizon, and unusual atmospheric conditions. The fixed offset cannot follow a daylight-saving switch within the date, and the site does not infer historical time-zone rules.
At high latitude, some dates have no sunrise or no sunset. Without both boundaries, the daylight-eighth method has no ordinary interval to assign. Regional almanacs may use a different fallback, but this calculator does not silently substitute one. Rahu Kalam itself is a traditional symbolic timing convention; this page makes no claim that the window exerts an astronomical force or guarantees an outcome.
Method: Drik Panchang, “Rahu Kalam”; astronomical rise/set API: Astronomy Engine 2.1.19.