Why does birth time matter?
In a birth chart, the Sun and planets barely change sign over the course of a day. The rising sign, however, changes roughly every two hours, and the house cusps move every few minutes. The Midheaven (MC), the point tied to career and public life, depends on the time as well. Without a birth time, about half of the chart stays out of reach.
If you know your birth time, you can go straight to the free birth chart calculator. If you don't, or you're unsure about the time you were told, this page is for you.
What is birth time rectification?
Rectification is a way of working backwards from real life events to an unknown or uncertain birth time. The idea is simple: turning points such as a marriage, a move, the loss of someone close or a new job tend to fall on dates when the sky makes strong contact with the time-sensitive points of the chart. The birth time that explains most of those events at once is the most likely one.
Astrologers traditionally do this by hand over many hours. For a step-by-step introduction to the method, see the lesson on rectifying a birth time.
How does this calculator work?
You enter your birth date, your birthplace and a window of up to 3 hours in which your birth time probably falls. Then you add between 3 and 15 life events, each with a type and a date. The calculator first scans the window in 5-minute steps. For every candidate time it builds the chart angles (Ascendant and MC) and scores how closely transits, solar arc directions and the progressed Moon touch those points on your event dates. It then rescans the area around the best candidates minute by minute.
You get the most likely time, up to three close alternatives and the rising sign for each. The calculation is purely mathematical and repeatable: the same details always give the same result. It uses the same method as the birth time finder in the Moon Shine app.
Which life events work best?
The most useful events are the ones you can date to the day and that changed the direction of your life: marriage or divorce, the birth of your first child, the loss of a parent, a major move or emigration, your first job, leaving a job, starting a business, graduation, a serious accident or surgery. These are the events most clearly linked to the chart angles.
Choosing events from different areas of life makes the result stronger. One or two events each from work, relationships, home and family work better than five job changes. If you're not sure of a date, leaving that event out is better than guessing. You can add more than one event of the same type.
How reliable is the result?
Every result shows an estimate clarity: high, medium or starting estimate. Clarity looks at three things: how wide your time window is, how many events you entered, and how many of them match this time clearly. With a window of up to 2 hours and at least 4 events, clarity is high as soon as one event matches clearly; with a 1-hour window, 3 events are enough.
A "starting estimate" doesn't mean "wrong". It shows the time where your events line up best, and tells you to treat it as a starting point because the window is wide or the events don't match clearly yet. More events and a narrower window make the result clearer. No rectification is certain; a birth certificate or hospital record is always the most reliable source.
Don't know your birth time? Where to look first
Before calculating, it's worth checking records. Depending on where you were born, the time may be on a long-form birth certificate or in a hospital record; a note in a family album can help too. Even asking a parent or someone who was there "was it morning or evening?" narrows the window. Then use this tool and draw your birth chart with the time you find. If a term is unfamiliar, the astrology glossary explains it plainly, and the free astrology academy takes you through it lesson by lesson.
Frequently asked questions
Is the birth time calculator free?
Yes. You can estimate your most likely birth time for free, with no signup and no email.
I have no idea of my birth time. Which window should I enter?
If your family remembers anything, enter a window of up to 3 hours around it. If there's nothing to go on, check your birth certificate or hospital record first. You can also try different windows separately.
How many events should I enter?
At least 3 and up to 15. Between 6 and 10 events that you can date to the day, from different areas of life, usually give the clearest result.
Is the result exact?
No. The result is the time where your events line up best within your window, and it is an estimate. The estimate clarity shows how distinct that estimate is. The time on a birth certificate is always more reliable.
Are my birth details and events stored?
No. Your birth date, place, time window and events are only used for the calculation and are not saved. No free text is asked for events; only the type and the date are sent.
What can I do with the time I find?
The button on the result screen carries the time straight into the birth chart calculator, so you can see your rising sign and houses. The birth time finder in the app explains the result and saves the time to your profile.
The birth time finder in the app runs the same calculation, explains the result and saves the time to your chart. Your full chart reading and chats with Selene are there too.