Short answer: A free calculator can produce the same chart as a paid one when they use matching inputs, methods and settings. Check solar-term boundaries, the convention around midnight, the time-zone conversion and any solar-time adjustment. A matching chart does not establish the validity of its personality or future interpretations.
Two calculators may disagree because they use different conventions, different data or a faulty implementation. A useful comparison starts with their stated settings, rather than which result feels more flattering.
1What "accurate" actually means here
Separate the calculation from the meaning assigned to it.
Chart calculation concerns how the eight characters are derived. Compare the same birth details and conventions, then trace any difference to the relevant calculation.
Interpretation concerns the traditional meanings assigned to those characters. Correct arithmetic does not demonstrate that a claim about someone's life is accurate.
You can inspect a calculator's inputs and outputs without accepting every interpretation attached to them.
Four settings to check
The solar term, not the lunar date
Bazi month boundaries use the relevant solar terms. A birth close to a boundary needs the term's time as well as its calendar date.
Check whether the tool documents its solar-term method. A missing display alone does not prove the calculation is wrong.
The hour branch and the midnight convention
The two-hour Rat branch crosses midnight. Schools differ on how to assign the day pillar around 23:00, so compare the selected convention before calling a result incorrect.
Use a made-up example near a branch boundary and change the time slightly. Check that the change matches the convention the tool documents.
Longitude, not just time zone
Some methods use civil time; others apply a local solar-time adjustment. A birthplace may be needed for that adjustment. Match the convention when comparing tools.
Check whether the tool uses a city, coordinates or another location input, and whether it states how that input affects the time.
Historical daylight saving
The clock recorded at birth may include daylight saving or a historical time-zone offset. These depend on the place and date.
Check the offset used for the specific place and date. A current time-zone label may not describe a historical birth correctly.
A practical comparison checklist
Use synthetic examples when testing a tool, and keep a note of the settings.
Repeat the same case. Matching inputs and settings should reproduce the same base chart. If they do not, check for saved values, default settings or a calculation error.
Test an hour boundary. Change the time across a known two-hour branch boundary and inspect the result under the tool's stated convention.
Test a solar-term boundary. Use times just before and after a documented term boundary and check the month pillar.
Compare like with like. Match the date, location, time conversion and day-boundary convention. If the charts still differ, investigate the calculation rather than averaging the results.
When a free chart may be enough
A tool's price is separate from the quality of its calculation. Clear settings and reproducible results are more useful checks.
If you want to see the chart components and learn the terminology, a free calculator may provide what you need.
A longer reading adds explanations and traditional interpretations. Paying for more detail does not make those interpretations verified facts about your life.
How to check Hour Light
You can explore Hour Light's chart tools before choosing a paid reading. Review the displayed inputs and settings, especially if you are comparing a result from another method.
The Personal User Manual is a separate 21-chapter reading based on the chart. It is a one-time purchase with no subscription.
If you find a difference you cannot explain, note the relevant settings and chart component when asking for help.
Explore the chart components
Start with a free chart
Enter the requested birth details, review the settings and explore the components before deciding whether you want a longer reading.
Free chart engine / Personal User Manual NT$3,600 one-time, no subscription
Frequently asked questions
Are free Bazi calculators accurate?
Often yes for building the chart, because that part is arithmetic rather than opinion. The common failures are using the lunar date instead of the solar term, ignoring the longitude of the birthplace, and mishandling births near 23:00. Check those three and you have checked most of it.
Why do two Bazi calculators give me different charts?
Almost always the solar term boundary, the hour branch convention around midnight, or a missing longitude correction. Ask each tool which solar term your birth falls in and whether it used your city, and the difference usually explains itself.
Do I need my exact birth time for Bazi?
For the hour pillar, yes. The other three pillars come from the date. If your time is uncertain, you still get a usable chart, but treat anything that depends on the hour as provisional rather than settled.
Does my birth city really change the chart?
It can. The chart runs on local solar time, and time zones cover a lot of longitude. For births close to an hour boundary, the correction is the difference between one hour pillar and the next.
Is a paid Bazi reading more accurate than a free calculator?
Not for the chart itself. A correct chart is a correct chart. What you pay for is the reading: the relationships between the pillars, the timing layers, and a consistent interpretation held across a long document.