If you know your birth time only roughly, enter the birth date and place above, the earliest and latest times it could have been, and up to four life events you are sure of. This free helper steps through that window, tells you first which rising sign each part of it gives, and shows where the rising sign (Lagna) and the navamsa (D9) Lagna change, where the Moon moves into a new nakshatra pada, and which dasha was running at each event and today if you were born at the earliest or the latest time, with the exact birth times at which those change. You then judge which stretch of time fits your life. The tool does not choose a time and does not say any time is the true one.
How it works
The rising degree is worked out from the NASA JPL DE440 tables used across this site and the sidereal time at the place, in the sidereal zodiac with the Lahiri ayanamsa, the same as our ascendant calculator. The navamsa follows the Parashari rule: each sign is cut into nine parts of 3 degrees 20 minutes, counted from the sign itself for a movable sign, from the 9th for a fixed sign and from the 5th for a dual sign, as on our navamsa calculator. The tool checks the Lagna and the navamsa Lagna every half minute through your window and pins each change to the second.
The dasha is Vimshottari, counted from the Moon’s place in its nakshatra at birth, with the same dates as our Mahadasha calculator. Because the Moon keeps moving, a later birth time moves every dasha date earlier. For each event the tool reads the main period and sub-period running at 12 noon that day, for a birth at the earliest and at the latest time, and finds the birth time at which the answer changes.
The method is the one P.V.R. Narasimha Rao describes in Vedic Astrology: An Integrated Approach (2000), ch. 32: try the times in the window and see which one explains the known past, starting with what changes fastest. He notes that most formula methods of rectification do not hold up, and that the corrected time is the one with which the known events of a life make sense.
Reading the result
The first line gives your rising sign for each stretch of birth time in your window, with the changes to the minute. The answer below it says how many times the Lagna and the navamsa Lagna change in your window, and how fast the Lagna moves there. The first table splits the window into stretches with one Lagna and one navamsa Lagna each, with the Lagna’s degree at each end. Then comes the Moon’s nakshatra and pada, and a table of the dasha at each event and today.
Some numbers from our own checks give a sense of scale. Rao’s rule of thumb is that the Lagna moves about one degree in four minutes. At Indian latitudes (we checked whole days from 8 to 35 degrees north, between 1900 and 2074), a navamsa Lagna lasts between about 8.5 and 16.3 minutes; far from the equator the spread is wider, from about 5.5 to 19 minutes at the latitude of London. Each minute of birth time moves all the dasha dates by the same number of days, between about 1.3 and 5.9: it depends on the lord of your birth nakshatra, whose period is running at birth, and on how fast the Moon was moving, from about 1.3 to 1.8 days for a nakshatra of the Sun to about 4.5 to 5.9 days for a nakshatra of Venus. The tool shows the actual figures for your own window.
Use the stretches as questions. Which Lagna describes your body and temperament? Did a major change fall in the sub-period one stretch gives and not the other? If two stretches fit equally well, the tool cannot settle it, and an astrologer may look at further divisional charts.
Where traditions differ
Rao lists several published rectification formulas, among them those based on the Pranapada lagna and on Kunda, and explains why he does not trust them: applied to twins born minutes apart, they give the same time or times far apart. Other teachers use them. This tool uses none of them and only lays out what changes. Teachers also differ on which events to trust and which divisional chart to read for each; Rao, for example, reads career from the D10 and education from the D24, which change even faster than the navamsa.
What it does not do
It does not rectify your birth time, rank the stretches or score how well an event fits. It does not draw the other divisional charts or use sign-based dashas. It keeps the window to one date, up to twelve hours long; for a window across midnight, run it once for each date. Births from 1900 to 2074 can be entered. Before 1951 the clock of a place comes from your browser’s time zone database, which can hold local mean time rather than the standard time then in use, so an old recorded time may need checking against the clock of the day.
What you type here stays in your browser and is not kept with your email. For the full dasha list of any one time, use the Vimshottari dasha timeline, and for all the divisional charts, the divisional charts calculator.
Frequently asked questions
↳ Can this tool find my exact birth time?
No. It shows how the Lagna, the navamsa Lagna and the dasha change across the window you give, so you can compare each stretch with your life. Choosing the time is your judgment, or an astrologer's.
↳ How wide should the window be?
As wide as your real doubt about the time, and a little wider to be safe. The tool accepts up to twelve hours on one date.
↳ Which life events help most?
Events whose dates you are sure of and that changed your life clearly, such as marriage, the birth of a child, a first job or a move abroad. The tool shows which dasha was running at each one for every stretch of your window.
↳ Why does the dasha change when the birth time changes?
The dasha is counted from the Moon's place in its nakshatra at birth, and the Moon moves about half a degree an hour. A later birth time puts the Moon further along, so every dasha date moves earlier, by a few days for each minute.
↳ Why does the navamsa Lagna change so often?
A navamsa is only 3 degrees 20 minutes of the zodiac, and the Lagna moves through it in minutes, so a small change of time can change the navamsa Lagna even when the Lagna itself stays the same.
↳ Is my data saved?
No. The window and the events you type stay in your browser. Only the place search asks another service, as on every tool here.