Why birth-chart calculators can disagree
Compare the inputs and conventions before comparing interpretations. A practical checklist for Astrologram and other calculators.
Astrologram · Reviewed ·
Start with the calculation settings
Different results do not by themselves show which calculator is correct. First check whether both tools received the same civil date, time, place, and time-zone information, then compare their zodiac, house, and node conventions.
A difference in interpretation is also separate from a difference in calculated coordinates. Compare the underlying settings and positions before comparing written meanings.
A comparison checklist
The right column describes this app’s current implementation. It is not a claim about the settings used by a particular other service.
| Compare | Astrologram currently uses |
|---|---|
| Birth time and time zone | Entered civil time converted with the selected IANA time zone |
| Zodiac | Tropical, using true ecliptic-of-date longitudes |
| Houses | Equal houses starting at the calculated Ascendant |
| North node | Mean-node formula |
| Unknown time or minute | Noon, or minute 00 of the selected hour |
| Major-aspect orbs | Sextile 6°; conjunction, square, trine and opposition 8° |
A fictional time-zone mismatch
Suppose a fictional birth is entered as 03:15 on 24 May 1998 in Hong Kong. With Asia/Hong_Kong, that civil time corresponds to 19:15 UTC on 23 May. Entering the same numbers as 03:15 UTC on 24 May instead represents a different instant, eight hours later.
Use the same civil time and correct location zone in both tools, or confirm that both are comparing the same UTC instant. Do not apply an offset manually and then ask the calculator to apply it again. Historical daylight-saving rules may also matter for other dates and places.
Check implementation limits too
Conventions do not explain every discrepancy. This app’s current midheaven output is the tenth equal-house cusp rather than an independent meridian Midheaven. Planet speeds and retrograde states are not fully calculated. Those fields should not be used as an accuracy benchmark.
The methods page documents these limits. If a difference persists after matching inputs and conventions, do not assume that either output is automatically validated by this checklist.
Make the comparison reproducible
Record the date, civil time and uncertainty, location, time zone, zodiac, house system, node type, and aspect orbs for both calculations. A screenshot without these settings may not explain a difference.
Keep private birth details out of public posts. You can use a clearly fictional example when discussing calculator behavior. Start a new chart, or correct a saved profile on the account page before selecting it again.