Don’t know your birth time, or not sure about it? A good part of your chart still holds. Here is what really moves, measured with our own engine.
Why the time matters
Your chart is built from the positions of 13 bodies when you were born, then about 88 days earlier. Most of them move slowly: the Sun changes gate every 5 to 6 days. The Moon crosses a gate in about ten hours. The Moon is the main reason time matters, along with the Sun’s lines, which set your profile.
What an hour changes, in numbers
We drew 2,000 random birth moments between 1950 and 2010, then recalculated each chart with the time shifted. Here is the share of charts where each item changes:
| Shift | Type | Authority | Profile | Defined centers | Any of the four |
|---|---|---|---|---|---|
| 15 minutes | 0.3% | 0.5% | 2.8% | 1.9% | 4.5% |
| 1 hour | 2.3% | 2.3% | 8.8% | 7.2% | 15.7% |
| 2 hours | 4.5% | 4.3% | 17.9% | 13.6% | 29.2% |
| 6 hours | 12.6% | 10.8% | 40.7% | 35.1% | 61.7% |
| 12 hours | 21.5% | 18.3% | 66.6% | 55.8% | 84.8% |
The takeaway: with a time that is right to within 15 minutes, your chart is almost always correct. With no time at all, your type stays the same in about 4 cases out of 5, while your profile becomes uncertain.
What our calculator does without a time
On the calculator, tick “I don’t know my birth time”. We then calculate your chart at noon and show separately what holds whatever the time that day, and what depends on it. That way you know what you can rely on.
Where to find your birth time
- Your birth certificate. In many countries the long-form version records the time. In France it always does; in the US and UK it depends on the state or nation.
- Hospital or maternity records, if your parents kept them.
- Your parents or a relative who was there. Their memory helps, but treat it as a range (“late morning”) rather than an exact time.
What about rectification?
Some practitioners offer to “rectify” your birth time by working back from events in your life. It is an astrology technique that assumes the system works, which has not been shown (see what we actually know). The result can’t be checked. A chart that is incomplete but honest is the better option.
If you are torn between two times, calculate both charts and read the page for each authority. For a week, jot down your decisions and how you made them. Whichever one matches your notes better gives you a clue. It stays a clue, though a firmer one than a gut feeling.