Birth time rectification: what it is
Birth time rectification is the traditional practice of estimating an unknown time by matching it with life events. It is a method that many practitioners use, and the results depend on the practitioner's judgement.
What it is
The usual approach is to pick events with known dates, such as marriages or job changes, and look for a Lagna that fits the dasha periods and the events. Because the method relies on interpretation, different practitioners can reach different times.
How it is worked out or read
This site does not perform rectification. The tools compute the chart for a given time, so a user who wants to test several times can enter each one and compare the results.
Where it appears on this site
The birth time accuracy article explains the stakes. The birth chart computes the chart for any time you enter.
What rectification means
Rectification is the attempt to estimate or correct a birth time when it is unknown or uncertain, using other information. The most common approach compares the timing of significant past events in a person's life with the dashas and transits that a candidate birth time would produce, and chooses the time whose chart fits the events best. Other approaches use physical description, the Lagna's traditional appearance, or special techniques from the texts.
Why it is uncertain
Rectification can be useful, but its results are much less certain than a recorded time. Different practitioners using different methods can arrive at different times for the same person. Because dashas and transits offer many possible matches for any event, it is often possible to find more than one time that seems to fit. And the method assumes that chart factors correspond to life events in a particular way, which is itself a matter of interpretation rather than measurement.
A careful approach
A careful rectification starts with the narrowest possible window from documents and memory, rather than from the whole day. It uses events whose dates are certain, such as marriage, the birth of children, a parent's death, relocation or major career changes, and it commits in advance to how each event should show in the chart, rather than finding a fit after the fact. It also reports the result with its uncertainty, for example 'most consistent with a time between 7:20 and 7:35, Lagna Mesha'.
What a rectified time can support
A rectified time can reasonably support readings that depend on the Lagna sign, if the window falls within one sign. It should not be relied on for fine work with divisional charts such as the D60, which change every few minutes, or for exact dasha sub-periods. The reader should keep a note that the time is rectified, by whom and by what method.
When to leave it
For many purposes, rectification is not needed. The Moon sign, the nakshatra and the planets' signs are usually certain from the date alone, and many readings can be built on them. If rectification would only add a false sense of precision, it is better to leave the Lagna open and say so.