Historical offset
The selected city supplies the UTC offset that applied on the birth date, including historical daylight-saving rules.
Free BaZi calculation tool · exact recorded birth time
BaZi True Solar Time Calculator
Convert the time on a birth record into apparent solar time before the BaZi Hour Pillar is assigned. The result separates historical time-zone offset, longitude, and the date-specific equation of time.
Review the calculation methodCivil time+Longitude+Equation of time=Apparent solar time
What the result means
Clock time and solar time are not always the same.
Civil clocks follow a shared time-zone meridian. Apparent solar time follows the sun's position at the birthplace on that date. The difference can be large enough to cross a two-hour BaZi boundary.
Longitude
Four minutes are added or removed for each degree between the birthplace and its civil time-zone meridian.
Equation of time
The seasonal difference between mean clock time and the sun's apparent motion is calculated for the entered date.
BaZi true solar time questions
Boundaries worth checking
What is true solar time in BaZi?
True solar time, also called apparent solar time, adjusts recorded civil time for the birthplace longitude and the seasonal equation of time. BaZi practitioners may use it before assigning the Hour Pillar.
Why can true solar time change the BaZi Hour Pillar?
Each Earthly Branch covers a two-hour period. If the correction moves a birth time across one of those boundaries, the Hour Branch and complete Hour Pillar can change.
Does this calculator account for daylight saving time?
Yes. For a supported city, the calculation resolves the historical IANA time-zone offset in force on the entered date, including daylight-saving rules, before applying longitude and the equation of time.
Can the corrected date change?
Yes. A correction near midnight can move the apparent solar time to the previous or next calendar date. The calculator shows that rollover explicitly because it may also affect the Day Pillar.
Is the true solar time result a complete BaZi chart?
No. It is the time-correction step only. A complete Four Pillars chart also resolves the exact Jie Qi year and month boundaries, Day Pillar, Hour Stem, Day Master, and element relationships.
Is this BaZi solar time calculator free?
Yes. The solar-time result is free and requires no account or email. The linked Four Pillars calculator also shows the chart and introductory reading for free; deeper interpretation is an optional one-time $4.99 unlock.