What a Kundli needs from you, and why the birth time matters most

A Kundli (जन्म कुंडली) is a map of the sky at the moment you were born, drawn as it looked from the place you were born. To draw it, three things are needed: the date, the time and the place. Nothing else is used — not your name, not your parents' names and not your current address.

Each of the three decides something different, and they are not equally forgiving when they are slightly wrong.

The date: where the slow planets were

The date fixes the positions of the planets that move slowly. Saturn spends about two and a half years in one sign, Jupiter about a year, and Rahu and Ketu about eighteen months. Get the date wrong by a day and those planets are, for practical purposes, in exactly the same place.

The Sun moves about one degree a day, so it is also stable across a day. The Moon is different, and it is where the chart starts to become sensitive.

The Moon: why the part of the day matters

The Moon crosses the whole zodiac in about 27 days, which is roughly 13 degrees every 24 hours. That is about the width of one nakshatra (13°20′). So the Moon changes nakshatra roughly once a day, and changes sign roughly every two and a half days.

This matters for two things people often ask about:

• The Dasha timeline. The Vimshottari Dasha sequence starts from the nakshatra the Moon was in at birth, and how far the Moon had travelled through it decides how much of the first period was left. A few hours on the clock can move the start and end dates of every period in your life.
• Guna Milan. All eight kootas in a match are worked out from the Moon. If the Moon changed nakshatra on the day you were born, the time of day decides which one you have.

The time: the ascendant and the houses

The lagna (ascendant) is the sign that was rising on the eastern horizon at the moment of birth. It moves fastest of all: on average the lagna changes sign about every two hours, and some signs rise in less time than that.

The lagna decides which sign sits in the first house, and so the arrangement of all twelve houses. Two people born on the same day in the same city, a few hours apart, can have the same planets in the same signs but in completely different houses. That is why an astrologer will usually ask for the birth time before anything else.

If your time is off by five minutes, the lagna usually stays the same. If it is off by an hour, it may not.

The place: the horizon and the time zone

The place does two jobs. It gives the latitude and longitude, which decide what was on the horizon — and so the lagna. And it gives the time zone in force on that date, which turns the clock time written on a birth certificate into a single instant in universal time.

That second job is easy to get wrong by hand. A birth in India today is simple, because the whole country uses one time zone, but a birth abroad — especially in a country that moves its clocks for summer — needs the rule that applied on that exact date, not the one in force today. JeevanDrishti looks the place up and applies the time-zone rules for the date of birth, so you only type the time as it was written down.

If you do not know your birth time

Many people do not have an exact time, and that is not a reason to skip the chart. What changes is how much of it can be relied on:

• The planets in signs are still reliable, because the slow planets do not care about the hour.
• The Moon's sign is usually reliable; its nakshatra may not be.
• The lagna and the houses are the parts that cannot be trusted without a time.

When you create a chart on JeevanDrishti you can say whether the time is exact, approximate or unknown. The chart page then tells you plainly which parts depend on the time, instead of presenting a guess as if it were measured. For matching, the Kundli Milan by date page goes one step further: if the Moon changed nakshatra that day, it shows you every answer the date allows rather than picking one.

How JeevanDrishti calculates the chart

For the curious, and for anyone comparing charts from two different websites:

• Planet positions come from the Swiss Ephemeris, the same astronomical data most serious astrology software uses.
• The zodiac is sidereal, with the Lahiri ayanamsa — the standard used by the Indian government's calendar reform committee and by most Indian astrologers. Western (tropical) charts sit about 24 degrees away from sidereal ones, which is why your Western "sun sign" is often one sign ahead of your Vedic one.
• Houses are whole-sign, which is how the North Indian chart diagram is drawn: each house is one whole sign.

If another site shows a slightly different chart, the ayanamsa and the house system are the first two things to compare.

Where to go from here

A Kundli is a description of the sky at one moment; it is a starting point for reading, not a verdict about your life. If you have your date, time and place to hand, it takes about a minute to create yours — and your Dasha timeline is drawn from the same three answers.