Daylight Saving Time: The Most Common Error in Overseas Ziwei Charts

What one hour actually costs

Start with the price, then work out how to avoid paying it.

Take someone born in March 1990, in the third lunar month, whose converted birth hour is the Si branch.

By the rule for placing the Life Palace: begin at the Yin palace for the first month and count forward to the third month, which lands on the Chen palace. From Chen, place the Zi hour and count backward to Si —

Branch	Zi	Chou	Yin	Mao	Chen	Si
Palace (counting back from Chen)	Chen	Mao	Yin	Chou	Zi	Hai

The Life Palace sits in Hai.

Now suppose that hour should have been the Chen branch, because daylight saving was missed. The same counting table stops one column earlier, at "Zi", and the Life Palace becomes the Zi palace.

The result: the Life Palace has moved one palace, all twelve palaces have shifted by one, and every hour-based star is misplaced — Wenchang, Wenqu, Dikong, Dijie, Taifu, Fenggao, Tianxing, Tianyao. The birth-year four transformations do not change, but the palaces they occupy all do.

This is not a detail being slightly off. It is a different chart.

Why DST ends up on the certificate

Daylight Saving Time works by moving the clock forward one hour through the summer, so that people rise earlier and burn less lighting.

The crucial point: the hospital clock, and therefore the time written on the certificate, is the shifted clock. A certificate reading 10:00 during the summer actually refers to 09:00 standard time.

Restoring it means taking that hour back off:

standard time = certificate time − 1 hour (northern summer)
standard time = certificate time − 1 hour (southern summer, i.e. October to April)

Only after that do you apply the longitude and equation-of-time corrections to reach true solar time.

Two worked examples, and how one hour flips a branch

Example one: Beijing, 4 July 1990, 10:00 (daylight saving was in force that year)

Approach	UTC	Mean solar time (116.41°E)	True solar time	Branch
Correct (subtract 1 hour)	01:00	08:45	08:41	Chen
DST missed	02:00	09:45	09:41	Si

Example two: Sydney, 15 January 1990, 09:30 (southern summer, AEDT)

Approach	UTC	Mean solar time (151.21°E)	True solar time	Branch
Correct (subtract 1 hour)	22:30 previous day	08:34	08:25	Chen
DST missed	23:30 previous day	09:34	09:25	Si

Both examples happen to fall across the 09:00 boundary. An hour of error often leaves the branch untouched — a birth at 15:00 is in Wei either way — but every chart has a narrow band of times where it flips. Since birth times across an overseas community are spread more or less evenly, that means roughly one chart in twelve is affected.

DST windows by country

The table below is organised by the rules in force at the time, for quick triage. Exact dates follow each year's official announcement.

Country / region	DST period	Zone change	Notes
United States, Canada	from 2007: second Sunday in March – first Sunday in November	UTC−5 → −4 (Eastern), and so on	1987–2006: first Sunday in April – last Sunday in October
United States, Canada	before 1987	rules differ year by year	1974–1975 began in January, a response to the oil crisis
European Union, United Kingdom	last Sunday in March – last Sunday in October	UTC+1 → +2 (Central Europe)	adopted country by country around 1981
Australia	first Sunday in October – first Sunday in April	UTC+10 → +11 (Eastern)	Queensland, Western Australia and the Northern Territory do not observe it
New Zealand	last Sunday in September – first Sunday in April	UTC+12 → +13	southern hemisphere, spans the new year
Japan	1948–1951	UTC+9 → +10	imposed during the Allied occupation; abolished in 1952
South Korea	1948–1960, 1987–1988	UTC+9 → +10	dropped after the 1988 Seoul Olympics
Taiwan	1945–1961, 1974, 1975, 1979	UTC+8 → +9	after 1974, restored only in isolated years
Mainland China	1986–1991	UTC+8 → +9	mid-April to mid-September; see the next section

Two questions, always in this order: did that place observe daylight saving in that year, and was that date inside the window? Both have to be yes before you subtract an hour. Check only one and you have even odds of getting it wrong.

Three edge cases that break the rule

① The hour spring skips

On the spring changeover in the northern hemisphere, 2:00 jumps straight to 3:00. That hour — 2:00 to 3:00 — does not exist on the clock.

If a certificate reads 2:30 and the date is the changeover day, the recorded time is impossible. Either the clock was not set correctly, or the date is off by a day. That contradiction has to go back to the hospital record. Do not resolve it by guessing.

② The hour autumn repeats

On the autumn changeover, 2:00 falls back to 1:00. The hour from 1:00 to 2:00 happens twice: first as 1:30 daylight time (the earlier UTC instant), then as 1:30 standard time (exactly one hour later in UTC).

A certificate that says only "1:30" is therefore ambiguous by a full hour, and the two instants may even fall in different branches. You have to ask: the first one or the second? Families rarely remember, but a labour record often carries relative timings — "delivered six hours after admission" — which can pin it down.

③ The southern hemisphere runs the other way

Australia, New Zealand and South America put their clocks forward from October to April, which is precisely the northern winter. The intuition that "summer is when daylight saving happens" fails completely for anyone born down there.

The relationship between birth month and daylight saving inverts accordingly: January, February and December births need the hour subtracted, while June and July births do not.

Mainland China, 1986–1991

This one is regularly overlooked, because the widespread assumption is that China never had daylight saving at all.

In fact mainland China observed it from 1986 to 1991: it began in mid-April each year and ended in mid-September, with clocks moved forward one hour (UTC+8 → UTC+9).

Which means:

Anyone born between May and early September in those years has daylight saving baked into the certificate time and must subtract an hour
On the 4 July 1990 example above, subtracting or not subtracting gives Chen or Si respectively (see the table)
People born in those six years are now roughly 35 to 40, which makes them a large share of anyone seeking a reading

Xinjiang is more involved still. The region has long used an unofficial "Urumqi time" (UTC+6) alongside official Beijing time, and daylight saving was layered on top of that from 1986 to 1991. For a birth in Urumqi you must first establish whether the family means Beijing time or Xinjiang time, then undo the daylight saving. Both steps, without skipping either.

How to verify a given date

In descending order of reliability:

Method	How	Coverage
IANA time zone database	`zdump -v Asia/Shanghai \| grep 1990`, or read the UTC offset for that instant with Python's `zoneinfo`	most authoritative; every change since 1970
timeanddate.com	enter the city and year, look under "Time Zone Changes"	graphical, with some material before 1970
The certificate itself	some countries print "DST" or "Daylight Saving Time" after the time	most direct, but not universal
Hospital delivery record	labour charts usually record absolute start and end times	most precise; requires a request to the hospital
Local newspapers of the year	look for the announcement of the switch dates	useful for periods before 1970

A quick check in Python (no network needed — zoneinfo ships with the historical data):

from datetime import datetime
from zoneinfo import ZoneInfo

t = datetime(1990, 7, 4, 10, 0, tzinfo=ZoneInfo("Asia/Shanghai"))
print(t.utcoffset())   # 9:00:00 → UTC+9, i.e. daylight saving in force

If utcoffset() returns 9:00:00 rather than 8:00:00, the date falls inside daylight saving and an hour has to come off.

Always use the zone name for the birthplace: America/Los_Angeles, Australia/Sydney, Europe/Madrid, Asia/Shanghai, Asia/Hong_Kong, Asia/Taipei. Looking up a Hong Kong birth under Asia/Shanghai introduces historical error, because the two sets of rules have not been identical since 1904.

The checklist

Before casting a chart for an overseas or historical birth, walk through this in order:

Is the certificate time the local clock time? (Not "Beijing time", and not something a relative already converted.)
Did that city observe daylight saving in the birth year?
Does the birth date fall inside the daylight-saving window?
If yes, subtract one hour to get standard time
Convert to UTC, then compute local mean solar time from the longitude of the birthplace
Add the equation of time to obtain true solar time
Is the result within ±10 minutes of a branch boundary? If so, cast both charts
If the time comes only from family memory, state the confidence level and avoid a single assertion

Steps 2 and 3 are the ones most often skipped, because they require actively looking something up rather than relying on common sense.

Scope and sources

This article deals with the technical problem of how times are recorded and converted. It makes no claims about fate or fortune. The site treats Zi Wei Dou Shu as a structural frame for self-understanding — a way to think about tendencies and circumstances — not as prediction, and not as a substitute for any form of professional advice.

Daylight-saving rules follow each country's announcements for the year in question; historical data can be checked against the IANA time zone database. The worked examples use standard astronomical formulas with the usual approximation for the equation of time, accurate to within a minute.

Frequently asked questions

My birth certificate does not mention daylight saving. Does that mean there was none?

No. The great majority of countries print only the time on a birth certificate and never note whether summer time was in force. What settles it is the rule that applied at that place in that year, not whether the document carries a label.

I was born in mainland China in 1990. Do I subtract an hour?

It depends on the month. Daylight saving ran from mid-April to mid-September in 1986–1991, so a birth inside that window needs the hour removed; a birth between October and March does not. Check the exact dates against that year's official announcement.

Can subtracting an hour change the date?

Yes. If the certificate reads 00:30 during daylight saving, removing an hour gives 23:30 on the previous day, which belongs to the previous day's Zi branch. Births that cross midnight need particular care here, because the date determines the position of the Ziwei star and one day of error throws off the whole chart.

How do I work out a birth in Australia?

Australia is in the southern hemisphere, so daylight saving runs from the first Sunday in October to the first Sunday in April. A January birth is therefore usually inside the window and needs an hour removed. The state matters too: Queensland, Western Australia and the Northern Territory do not observe it, so the same date there needs no adjustment.

Do I need to check Japan or Korea?

Japan observed daylight saving only from 1948 to 1951 and abolished it in 1952; Korea observed it from 1948 to 1960 and again in 1987–1988. If your birth year falls outside those ranges, daylight saving is not a factor, but the longitude correction still applies.

What about Hong Kong and Taiwan?

Hong Kong observed daylight saving on and off between 1941 and 1979 and dropped it from 1980. Taiwan observed it from 1945 to 1961 and again in 1974, 1975 and 1979. Anyone born in those years needs the exact start and end dates for that particular year.

If daylight saving was missed, will the chart be obviously wrong?

Not necessarily, and that is exactly what makes it dangerous. If the original time sits in the middle of a branch, say 15:00, removing an hour still leaves it in Wei and nothing changes; only times near a boundary flip. So "I had it done years ago and it seemed right" is not evidence that the hour was handled correctly. Either verify it, or admit the uncertainty.

Could daylight saving and the longitude correction cancel each other out?

In principle, yes, but you cannot count on it. The direction of the longitude correction depends on where the birthplace sits relative to its standard meridian: Los Angeles is east of 120°W, giving +7 minutes, which stacks on the same side as the −60 minutes from daylight saving; Madrid is far west of 15°E, giving −75 minutes, also on the same side. Cancellation would require a very particular longitude, and should never be assumed in practice.

Content on this site is compiled from classical sources for self-reflection and cultural research. It is not prediction, medical, legal or investment advice.