Your ascendant, and how much your birth time moves it

What this tool computes

The lagna, or ascendant, is the point of the zodiac rising on the eastern horizon at the moment and place of your birth. This tool reports which sign that is and the exact degree within it. It also reports a second number: how many minutes your recorded birth time would have to be wrong, in either direction, before the rising sign became a different sign.

Signs do not rise in equal time

The common rule of thumb is that the lagna changes about every two hours. That is an average over the whole day, and it is not true of any particular birth. Because the zodiac is tilted relative to the celestial equator, some signs climb the horizon steeply and some at a shallow angle. At Indian latitudes the difference is large: certain signs take well over two hours to rise, and others are gone in appreciably less than ninety minutes.

So the honest answer to “how accurate does my birth time need to be” is not a general figure. It depends on the sign and on the latitude, and it is computable. That is the second number on this page, worked out for your birth rather than quoted from a rule of thumb. A birth in the last few minutes of a rising sign is a chart whose houses should be treated with real caution.

What the lagna decides, and what it does not

The lagna contributes nothing at all to the thirty-six-point guna score. Ashtakoota is computed from the two Moons; a lagna could be unknown and the score would be unchanged. Where it becomes decisive is mangal dosha, because traditions disagree about which point Mars is judged from — the Moon, the lagna, or Venus.

Our census measured both halves of that disagreement separately. Changing which houses a school counts moves the share of charts called manglik by 3 percentage points. Changing the reference point moves it by 29.

The argument about manglik is not mainly an argument about houses. It is an argument about where you stand to look at Mars.

A report that names a house list but not a reference point has disclosed the smaller half of its method. Across documented schools the manglik rate runs from 11.7% under Astro-Vision (serious Kuja dosha only) to 73% under OP / SKU panchangas. Which of those a chart falls under is a question about the school, not about the person.

My birth time was written down to the nearest five minutes. Is that enough?

Frequently, yes. Rounding to five or even fifteen minutes leaves the rising sign untouched in most charts, because most births are not near a boundary. The number this page gives you says whether yours is one of the exceptions, which is a more useful thing to know than a general reassurance.

Does the lagna change my guna milan score?

No. Not by a single point. It does enter the navamsha chart, which many traditions weigh heavily for marriage, and it enters mangal dosha under the schools that judge Mars from the ascendant. So it can matter a great deal to a verdict while mattering not at all to a score.

What if the birth time is genuinely unknown?

Then there is no lagna and there are no houses, and that should be stated rather than worked around. Nakshatra-based matching remains computable, since it needs only the Moon. A report that prints a confident ascendant for a birth with no recorded time has assumed one, and is worth asking about.