How to calculate Rahu Kalam yourself, step by step

What you need

You need three pieces of information to calculate rahu kalam. You need to know what time the sun rises where you live. You need to know what time it sets. And you need to know the weekday.

Everything else is arithmetic. No tables, no almanacs, no app. Just addition, subtraction and division by eight.

Step 1, Find the daylight span

Daylight is the entire stretch from sunrise to sunset.

Write down sunrise in minutes past midnight. Do the same for sunset. Subtract the first from the second. The result is today's total daylight, measured in minutes.

In Chennai on 14 January 2026 (a Wednesday) the sun rises at 06:35 and sets at 18:00. Daylight lasts 685 minutes, or 11 hours and 25 minutes.

Step 2, Divide by eight

Daylight is split into eight equal parts. Each part is one eighth.

Take the minutes from step 1 and divide by eight. In our example: 685 ÷ 8 ≈ 85.6 minutes. That is roughly 1 hour and 26 minutes per part.

Part 1 starts at sunrise. Part 2 starts when part 1 ends. And so on, until part 8 ends at sunset.

Step 3, Look up the weekday's part

Every weekday has its own fixed part number. The same number applies every single year.

Here is the complete table. It never changes, it is the same regardless of season, country or city. The only thing that changes is how long each part lasts, because daylight varies.

Step 4, Calculate start and end

Now you have everything. Multiply the part number by the part length, and add it to sunrise.

The start time is sunrise plus (part number minus 1) times the part length. The end time is sunrise plus the part number times the part length.

Here is the complete calculation for our example, Wednesday 14 January 2026 in Chennai:

What if the day is longer or shorter?

In January in Chennai, daylight lasts 685 minutes. That gives parts of roughly 86 minutes, about an hour and a half. Most people know rahu kalam as lasting about ninety minutes, and in South India that is close enough.

But in June, daylight in Chennai lasts 773 minutes, and each part grows to about 97 minutes, over an hour and a half. In London the difference is even bigger: a summer day can give parts of over two hours.

The rule does not change. It is the daylight that changes, and with it the length of each part.

What about Yamagandam and Kuligai?

Rahu kalam is the best-known window, but it is not the only one. Yamagandam and kuligai are two more periods considered inauspicious. They are calculated the exact same way, you divide daylight into eight and use a different part number.

All three divide daylight into eight. So all three are the same length on any given day. And all three shift in the same way when daylight changes.

Try it with your city

Pick two cities below and see today's rahu kalam side by side. The calculator uses exactly the same formula as the steps above, just with your city's sunrise and sunset.

Five things people often get wrong

1. 'Rahu kalam is always ninety minutes'

Only when daylight is exactly twelve hours. That is rare. In South India it is close, but in Northern Europe the window can be over two hours in summer.

2. 'You can look it up in a fixed timetable'

Those timetables are computed for one city. Use them somewhere else and you will be off. Calculate it yourself, or use our calculator.

3. 'It is the same as Rahu hora'

No. Rahu hora (horai) is a different time period. Horai divides the day into planetary hours, not into eight. The two can overlap, but they are not the same system.

4. 'Daylight saving changes the calculation'

Daylight saving moves the clock, not the sun. Sunrise and sunset are already adjusted for daylight saving in every weather service. So no, the calculation is unchanged. You will not even notice.

5. 'It applies to the whole globe at once'

Rahu kalam depends on local sunrise. Toronto and Chennai do not have rahu kalam at the same clock time, because the sun does not rise at the same moment in both places.