What your birth time actually changes in a chart

Almost every week someone tells us, apologetically, that they only know their birth time to within an hour. They expect to be turned away. They rarely are — but the apology is worth taking seriously, because the answer to “how much does it matter” is genuinely different depending on what you are asking.

Start with what birth time does not change. The positions of the slow-moving planets — Jupiter, Saturn, Rahu and Ketu — barely shift over a day, let alone an hour. The sign each planet occupies is almost always stable across a wide window. If your question is about long-term patterns, an hour of uncertainty changes very little.

What birth time does change is the ascendant, and therefore the entire house structure. The ascendant advances through roughly one degree every four minutes, and a full sign every two hours. Get the time wrong by ninety minutes and you may have the wrong rising sign — which reorders all twelve houses and reassigns which planet governs which area of life.

This is why career and marriage questions are the most time-sensitive. Both depend on specific houses — the tenth and the seventh — and if the house cusps have shifted, the reading shifts with them. A chart with the wrong ascendant is not slightly wrong; it is answering a different question.

When the time is genuinely unknown, there are two honest routes. Birth-time rectification works backwards from dated life events — a marriage, a move, a bereavement, a job change — and narrows the window until the chart accounts for what actually happened. It is slow and it needs your cooperation, but it works.

The second route is Prashna, which sidesteps birth data entirely by casting a chart for the moment a sincere question is asked. It answers that one question well and does not pretend to be a full life reading. For a great many enquiries, that is exactly what was wanted anyway.