Birth time in a kundli: how much it changes, measured

The question has no single answer, and that is the answer

“How accurate does my birth time need to be?” is asked as though the chart were one object that is either right or wrong. It is not. Different parts of a chart are computed from different things, and they fail at completely different rates.

Planetary positions come from the date and the time of day, and planets move slowly — fifteen minutes barely touches them. The ascendant comes from the Earth's rotation, which moves a full sign every two hours, so it is far more fragile. And the divisional charts are computed from the degree within a sign, so they are the most fragile of all.

What we measured

We ran 143 charts — twelve cities from 8.5°N to 34°N, birth years from 1952 to 2005, birth hours spread across the day — and shifted each birth time by one, five, ten and fifteen minutes in both directions, counting how often each part of the chart changed.

At fifteen minutes: the current mahadasha lord changed in 2.1% of charts and the Atmakaraka in 2.1%. The ascendant sign changed in 14.0% and the current antardasha lord in 16.1%. The Dashamsa ascendant changed in 99.3%, and the Navamsa ascendant in 100% — every single chart.

At one minute the Navamsa ascendant had already changed in 9.8% of charts. That is the number worth sitting with: a birth time wrong by sixty seconds moves the D9 ascendant in one chart in ten.

What follows for a reading

A timing reading built on the mahadasha is robust to an uncertain birth time. A Sade Sati reading is robust, because it is counted from the Moon. An Atmakaraka reading is robust. A career reading built on the Dashamsa is not. A marriage reading built on the Navamsa is not.

This is why our checkout asks whether your time is exact, approximate or unknown, why the engine flags a low-confidence ascendant, and why a report built on an approximate time leans on the Moon. It is also why we publish these numbers: a reader is entitled to know which half of a reading rests on a time they are guessing at.

Common questions

How accurate does my birth time need to be?

For the dasha sequence and anything read from the Moon, within about half an hour is fine. For the ascendant and house placements, within a few minutes. For the Navamsa and the finer divisional charts, to the minute — which is rarely available.

Does one minute really matter?

For most of a chart, no. For the Navamsa ascendant, yes: it changed in 9.8% of our 143 test charts at a shift of a single minute.

Where do these percentages come from?

From our own benchmark over 143 charts, perturbed by ±1, ±5, ±10 and ±15 minutes. The script is deterministic and re-running it reproduces the table.

What if I do not know my birth time at all?

A Moon-based reading is still honest and useful — rashi, nakshatra, dasha, Sade Sati and the Atmakaraka all survive. The ascendant and the divisional charts do not, and no reading should pretend otherwise.