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Data quality and method

How accurate must a birth time be for an astrology chart?

Birth-time accuracy matters most for the Ascendant, Midheaven, houses, and time-sensitive Moon positions; the safe interpretation must match the data quality.Reviewed · 2026-08-24 · Educational astrology content
Direct answer

There is no single safe error margin for every chart. The Ascendant moves at a variable rate by latitude and zodiac region, so even a short error can change its degree; an error of hours can change the rising sign or house structure. If the time is unknown, avoid houses and angles.

Key points

  • Recorded time and remembered time are not equally reliable.
  • Historical daylight-saving rules can shift the actual instant.
  • The Moon moves much faster than the outer planets.
  • A precise-looking time is not proof of a precise record.

Method

  1. Label the source: record, written family note, broad memory, or unknown.
  2. Calculate a range around the uncertain time.
  3. Keep only placements that remain stable across the tested range.

Limits and responsible use

  • Do not infer a precise time merely because one chart description feels accurate.
  • Rectification is a hypothesis, not independent proof.

Sources and references