How Daylight Saving Time Affects Your Chart: Getting the Hour Right Under DST

The Core Principle: The Clock Moved, the Sun Didn’t

Daylight Saving Time simply pushes clocks one hour ahead — the sun’s position doesn’t change at all. Since the Chinese double-hour is fundamentally about the sun’s position (True Solar Time):

A clock time that falls within DST must first have one hour subtracted to recover standard time, before applying the longitude and Equation-of-Time corrections.

Skip this step and the hour has a good chance of landing in the wrong slot — e.g. a 3:30 PM DST clock reading looks like the Shen hour, but the recovered 2:30 PM is actually Wei.

When You Must Handle It — and When You Don’t

Scenario	Subtract the hour yourself?
Charting the present moment (with the AI charting tool)	❌ No. Your device’s time zone already encodes DST; the True Solar Time engine anchors to it automatically
Manually converting a birth time (fixing the BaZi hour)	✅ Yes. If the birth certificate time falls inside that year’s DST window, subtract one hour first
Re-casting a historical moment	✅ Yes, using the DST rule in force at that time and place

DST Rules Quick Reference

US / Canada: second Sunday of March, 2 AM → first Sunday of November, 2 AM (the rule since 2007; from 1987–2006 it started the first Sunday of April). Most of Arizona and all of Hawaii observe no DST.
Europe: last Sunday of March → last Sunday of October.
Australia (south-eastern states): first Sunday of October → first Sunday of April (the southern “summer” straddles the new year); Queensland, WA and NT observe no DST.
Mainland China: DST was observed from 1986 to 1991 (roughly mid-April to mid-September). Anyone born in those windows must subtract an hour first — the single most common historical trap in Chinese charts.

Worked Example: Born in Beijing, July 1988

Clock time 12:20 on 1988-07-20 in Beijing:

1988 falls in China’s DST years → subtract one hour = 11:20 standard time;
Beijing sits at 116.4°E against the 120°E reference → subtract ~14 minutes ≈ 11:06;
The late-July Equation of Time is about −6 minutes → True Solar Time ≈ 11:00, right on the Si/Wu hour boundary.

Miss the DST correction in a boundary case like this and the Wu hour gets recorded as Wei — a completely different natal chart.

If You Can’t Memorize the Rules

Historical DST rules are fiddly (and have been amended repeatedly). Practical advice: take birth times from the birth certificate, use a charting tool that handles time zones automatically for present-moment charts, and when fixing a historical hour, search “year + place + DST” once to confirm that year’s rule.