You need your exact birth time for your rising sign (Ascendant) and your twelve houses, which shift about one degree every four minutes and change sign about every two hours. Your Sun sign and most planets do not need the time, because they move slowly. A time within 15 minutes is good enough for most charts.
What changes with the birth time?
| Part of the chart | Moves about | Needs your birth time? |
|---|---|---|
| Ascendant and Midheaven | 1° every 4 minutes | Yes, the closer the better |
| The 12 houses | With the Ascendant | Yes |
| Part of Fortune | With the Ascendant | Yes |
| Moon | 1° every 2 hours | Only if it changed sign that day |
| Sun, Mercury, Venus, Mars | About 1° a day or less | Rarely |
| Jupiter to Pluto | Much less than 1° a day | No |
Where can you find your birth time?
In the United States, the long-form birth certificate (often called the "certificate of live birth") usually shows the time of birth. The short version may not. You can order the long form from the vital records office of the state where you were born; Missouri's health department and New York City both describe it.
Other places to look:
- Ask your parents or relatives. Many people remember the hour, especially if it was early morning or late at night.
- Baby books, birth announcements and hospital bracelets. These often note the time.
- Hospital records. Some hospitals keep birth records and can share them with you on request.
What if you do not know your birth time?
You can still get a useful chart. Without a time, a birth chart is usually calculated for noon, which keeps every planet within a few degrees of its true place. What you lose is the rising sign, the houses and anything that depends on them.
In our report, if you tick "I don't know my birth time", we leave out the houses, Ascendant, Midheaven and Part of Fortune and say so clearly, instead of guessing. If the Moon changed sign on your birth day, we show both possible Moon signs.
What if your birth time is only approximate?
A time within 15 minutes is good enough for most purposes: the Ascendant moves about 4° in that time, which rarely changes its sign. If you were born close to a sign change, the rising sign may be uncertain, and it helps to read the profiles of both signs.
How do we use your birth time?
We convert your local birth time to Universal Time with the historical time zone of your birth city on that date, including daylight saving time. This matters: time zone rules have changed many times, and a one-hour error moves the Ascendant by about 15°. Our methodology page explains the full process.
Try it with our free birth chart calculator, or get the full natal chart report for 20 crystals (about $1).