How often do BaZi calculators get your chart wrong?
We simulated 120,000 birth moments in 12 cities, born between 1960 and 2009, and compared three common calculator shortcuts with an exact calculation, pillar by pillar.
Key findings
- About 30% of people born in New York, Los Angeles, Chicago, Toronto, Vancouver or London (29.8–30.8% by city) get at least one different pillar from a BaZi calculator that reads the clock time literally, times the solar terms in Beijing time and starts the year at Chinese New Year.
- Ignoring daylight saving time alone changes the hour pillar for 27.3% of US births and the Day Master itself for 2.2%.
- Starting the year at Chinese New Year instead of Start of Spring (立春) changes the year pillar for 2.0% of all births, and for 12.5% (about 1 in 8) of people born in January or February.
- Timing the solar terms in Beijing time instead of at the actual moment of birth changes the month pillar for 1.7–2.0% of people born in North America.
- Using true solar time instead of clock time changes the hour pillar for 6.2% of New York births, but 43.6% in Singapore and 63.1% in Madrid, whose clocks run far from the sun.
The three shortcuts
1. Reading the clock literally
BaZi hours are two-hour blocks tied to the sun. During daylight saving (summer) time the clock runs an hour ahead, so about half of summer births land in the wrong hour pillar if the calculator doesn't remove it — and clock times between 23:00 and midnight move into the next day, which changes the Day Master. 55% of the US births we simulated happened during summer time; daylight-saving rules have changed many times since 1960, so a calculator needs the rules in force on your birth date, not today's.
2. Timing the solar terms in Beijing time
The month pillar turns at twelve solar terms (节气), which are moments in time — the same instant everywhere on Earth. A calculator that feeds your local clock time into a Chinese calendar effectively treats you as born in Beijing. For someone born in New York that is twelve or thirteen hours off, enough to flip the month pillar for births close to a solar term. The month pillar is the birth season, the single heaviest influence on how strong a Day Master is.
3. Starting the year at Chinese New Year
Popular zodiac charts change the animal at Chinese New Year, a lunar date between 21 January and 20 February. BaZi changes the year pillar at Start of Spring (立春), around 4 February. Between the two dates the year pillar — including the animal — disagrees: 2.0% of all births and 12.5% of people born in January or February.
Results by city
| City | Any pillar differs¹ | Hour pillar, summer time ignored | Day Master, summer time ignored | Month pillar, Beijing-time terms | Hour pillar, true solar vs clock² |
|---|---|---|---|---|---|
| New York | 30.4% | 27.4% | 2.2% | 1.7% | 6.2% |
| Los Angeles | 30.3% | 27.2% | 2.2% | 2.0% | 7.3% |
| Chicago | 30.5% | 27.4% | 2.2% | 1.8% | 8.3% |
| Toronto | 29.9% | 26.9% | 2.1% | 1.7% | 15.4% |
| Vancouver | 29.8% | 26.6% | 2.1% | 2.0% | 11.6% |
| London | 30.8% | 28.2% | 2.2% | 1.1% | 8.6% |
| Paris | 21.0% | 18.5% | 1.5% | 0.9% | 43.5% |
| Madrid | 21.9% | 19.3% | 1.6% | 0.9% | 63.1% |
| Sydney | 16.5% | 15.2% | 1.1% | 0.4% | 6.1% |
| Singapore | 1.9% | 0.0% | 0.0% | 0.1% | 43.6% |
| Hong Kong | 11.1% | 9.2% | 0.7% | 0.0% | 21.2% |
| Beijing | 4.3% | 2.4% | 0.2% | 0.0% | 12.6% |
10,000 simulated births per city. ¹ A calculator using all three shortcuts compared with an exact clock-based chart (daylight saving removed, exact solar terms, year from Start of Spring); true solar time is not counted. ² A convention rather than an error — see below. Singapore and Beijing are controls: Singapore has no summer time and Beijing only had it from 1986 to 1991.
What about true solar time?
Many practitioners convert the birth time to true solar time — where the sun actually was at the birthplace, corrected for longitude and the equation of time. Others use standard clock time. Because this is a matter of convention, it is not counted as an error above. But it matters a great deal in some places: a clock-based and a solar-time chart disagree on the hour pillar for 6.2% of New York births, 43.6% in Singapore and 63.1% in Madrid, where the clock runs over an hour ahead of the sun. FateBook uses true solar time and shows the solar time it used in every chart's calculation details.
Why one pillar matters
A BaZi chart has eight characters in four pillars, and each pillar is read in relation to the others. The stem of the day pillar is your Day Master — change it and every reading changes. The month pillar carries the most weight in deciding whether a Day Master is strong or gentle. The hour pillar holds a quarter of your Five Elements balance. One wrong pillar is not a detail.
How to check your own chart
- Does the calculator ask for your birth city? A time zone alone can't apply historical daylight-saving rules or true solar time.
- Born during summer time? Check that the calculator removes it. If two calculators disagree on your hour pillar by exactly one step, this is the usual reason.
- Born in January or February? Check your year pillar against the date of Start of Spring in your birth year, not Chinese New Year.
- Born within a day of a solar term? Your month pillar depends on the exact minute; it needs a calculator that times terms from your actual birth moment.
- Born between 22:00 and 01:00? Your Day Master may depend on the day boundary (23:00 in most schools) and on the exact time conversion. More on birth times.
Method
- Sample. 10,000 birth moments per city, with dates uniformly distributed from 1 January 1960 to 31 December 2009 and clock times uniform over the day; times that never existed (skipped when clocks spring forward) were excluded. The simulation is seeded (20261014) and reproducible.
- Reference. The FateBook chart engine: solar terms computed for the exact birth instant, historical time-zone and daylight-saving rules from the IANA time-zone database, day pillar turning at 23:00.
- Limitations. Real births are not spread evenly across the day, and different schools of BaZi differ on details such as the day boundary. Figures are the share of births whose pillar characters differ; they don't measure how much a reading would change.
- Data. Download the results as JSON.
Cite as: FateBook (2026). How often do BaZi calculators get your chart wrong? fatebook.si/research/bazi-calculator-accuracy
Check your chart with the exact method
Your birth date, time and city — the four pillars with historical time zones, exact solar terms and true solar time. Free, in about two minutes.
Calculate my chart — freeFrequently asked
Do online BaZi calculators give wrong results?
Often, for some pillars. In FateBook's simulation of 120,000 birth moments, a calculator that reads the clock time literally, times the solar terms in Beijing time and starts the year at Chinese New Year gave about 30% of people born in the US, Canada or the UK at least one different pillar than an exact calculation.
Does daylight saving time affect my BaZi chart?
Yes, if you were born while daylight saving (summer) time was in force. Clocks were an hour ahead of standard time, so about half of those births belong in the neighbouring two-hour pillar. Ignoring it changed the hour pillar for 27.3% of US births and the Day Master for 2.2%. A good calculator removes daylight saving using the rules in force on your birth date.
Does the BaZi year start at Chinese New Year?
No. In BaZi the year pillar changes at Start of Spring (立春), around 4 February. Chinese New Year falls between 21 January and 20 February, so the two disagree for 2.0% of all births and 12.5% of people born in January or February.
Should a BaZi chart use true solar time?
Many practitioners convert birth time to true solar time — the sun's actual position at the birthplace — and others use standard clock time. It is a convention rather than an error, but it matters most where clocks run far from the sun: it changed the hour pillar for 6.2% of New York births and 63.1% of Madrid births. FateBook uses true solar time and shows the solar time it used.
How can I check if my BaZi chart is correct?
Use a calculator that asks for your birth city (not just a time zone), removes daylight saving time for your birth date, changes the year at Start of Spring, times the month pillar from the exact solar term, and starts the day at 23:00. Compare the four pillars from two such calculators; if they disagree, check whether you were born near a two-hour boundary, 23:00, a solar term or during summer time.
FateBook is designed for reflection and entertainment. BaZi is a traditional cultural framework; readings describe tendencies, not certainties, and are not medical, legal or financial advice.