How accurate does my birth time need to be? What if I don't know it?

within a few minutes is ideal; without a time you can still use the Moon sign and nakṣatra, or ask for birth-time rectification.

The ascendant degree moves about 1° every four minutes, so a difference of 10–15 minutes can shift house cusps and divisional charts like the navāṁśa, and near a sign boundary it can even change the lagna. The planets themselves move slowly, so their signs rarely change with a small error.

The best sources are a hospital record, a birth certificate or a note written by parents at the time. Phrases like “around sunrise” or “after lunch” give a range, not a moment.

If you have only the date, the Moon sign, nakṣatra (if the Moon did not change nakṣatra that day) and planetary transits are still usable. A careful astrologer can try rectification — testing the chart against known life events — but it is an estimate. Be wary of anyone who gives very precise predictions from a doubtful time.

Source: modern practice · Ascendant moves ~1° per 4 minutes

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