True Solar Time Calculator for BaZi
Why clock time is not enough for accurate BaZi. Learn how to calculate True Solar Time using Longitude and the Equation of Time (EoT).
BaZi (Four Pillars of Destiny) is deeply rooted in the solar calendar. To get an accurate chart, we must use the True Solar Time (TST) at the place of birth, not just the standard civil time shown on our clocks.
The Conflict: Clock vs. Sun
Modern countries use timezones to standardize time over huge regions. However, the Sun doesn't care about bureaucratic boundaries! If you are born at 12:00 PM in Paris, the Sun reached its peak at a different moment than if you were born at 12:00 PM in Strasbourg, even though both cities use the same clock time.
For BaZi, the Hour Pillar changes every 120 minutes. If your clock says 1:05 AM but the solar adjustment is -10 minutes, your "Solar Birth" was actually at 12:55 AM—potentially shifting you into a completely different Hour Pillar and even a different Day Master!
The Two Critical Corrections
1. Longitude Correction (LMT)
Every degree of longitude east or west of your timezone's standard meridian shifts the solar time by exactly 4 minutes.
- If you are East of the meridian, the Sun arrives earlier (+).
- If you are West of the meridian, the Sun arrives later (-).
2. Equation of Time (EoT)
The Earth's orbit around the Sun is not a perfect circle, and its axis is tilted. This causes the Sun's position to vary slightly throughout the year. This adjustment can add or subtract up to 16 minutes depending on the month.
The Formula
To calculate Standard BaZi Time, we combine these corrections:
$$Solar Time = Clock Time + (Long_{Birth} - Long_{Meridian}) \times 4 + EoT$$
- Find your Standard Meridian (e.g., UTC+1 = 15°E).
- Calculate the Longitude Gap.
- Apply the Astronomical EoT for the specific date.
How to use this Calculator
Use the interactive tool below to crunch the numbers for any date and location. We resolve the timezone, find the standard meridian, and apply the astronomical Equation of Time for you.
Interactive Solar Calculator
Precise BaZi Alignment
Coordinates determine your specific solar meridian.
Enter your birth details and click calculate to see the magic happen.
Relative Solar (Safe Standard)
The Standard BaZi Mode. It aligns solar reality with your current timezone pulse. Most professional software uses this to ensure the Day Master doesn't shift unexpectedly while still respecting local longitude.
True Sundial (Classical)
Pure astronomical time. It ignores modern timezones entirely. Use this if you are a Classical Practitioner who calculates based on the actual height of the sun in the sky, regardless of civil clocks.