Birth chart generator checklist: eight tests we ran on our own

A birth chart generator can look beautiful and still be wrong. The wheel is easy to draw. The hard part is the clock, the maths and the honesty behind it. Here are eight tests that work on any tool, and the result of running each one on ours. Charthood scored 12 out of 16, and we show where it lost points.

What makes a good birth chart generator?

Three things, in order. It converts your birth time to universal time correctly. It takes its planet positions from a source you can check. And it tells you its choices, such as the house system, instead of hiding them. Looks come last.

Each test below has the same shape: what to check, what we ran, what came out, and a score of 0, 1 or 2. A 2 means the tool passes. A 1 means it passes with a catch we can name. A 0 means it fails. We used Robin, one of our fictional example people, born at 8:30am on 14 March 1990 in Chicago, as the test subject. We scored ourselves, so check our working. Everything is UTC unless stated.

The eight tests, run on Charthood

1. Time zone history

Check: does the tool know what the clocks did in your birth year? Put in the same morning clock time in two different winters.

We ran: 09:00 in New York on 15 January 1974 and again on 15 January 1975. The US ran daylight time all year in the 1974 winter, so the two years differ.

Result: the tool used UTC−4 in 1974 and UTC−5 in 1975, which puts the 1974 Rising at 6°15′ Aquarius and not 27°37′ Aquarius. It reads the IANA time zone database for the birthplace and prints the offset under the chart title. Score: 2.

2. House system disclosure

Check: does the chart name its house system, and can you change it? Different systems put planets in different houses.

We ran: Robin in all four systems Charthood offers. Compared with Placidus, Whole sign moves 2 of Robin’s 11 planets and points into another house. The chart caption reads “Placidus houses.” and the PDF repeats it.

Result: the system is named. But the choice of Whole sign, Equal or Porphyry lives in the edit form of a saved chart, so you need a free account. The first chart you make has no switch. Score: 1.

3. Node type

Check: is the North Node the true node or the mean node? Many tools never say.

We ran: both at Robin’s birth moment. The true node is 15°51′ Aquarius and the mean node 14°36′ Aquarius, 1°15′ apart. The chart shows 15°51′ Aquarius, so it uses the true node.

Result: our accuracy page and the North Node guide both say “true node”. The chart itself just says “North Node”. A reader who never visits those pages won’t know. Score: 1.

4. Orbs

Check: does it say how close counts as an aspect? Wide orbs find aspects everywhere.

We ran: Robin’s aspects under our orbs, then under a flat 10° for everything. Ours finds 19 aspects. A flat 10° finds 35. The chart prints each aspect’s orb, tightest first, and our aspects guide lists the rule: about 7° for the main aspects, a degree more with the Sun or Moon, 4° for sextiles, less for the slow outer planets and the node.

Result: orbs are shown and published. They are also fixed. You can’t widen or narrow them, and the on-page list shows only the 12 tightest. Score: 2.

5. Source of positions

Check: does it name its ephemeris, and has anyone compared it with a reference? See our ephemeris explainer for why this matters.

We ran: Robin’s Sun and Moon against NASA’s JPL Horizons at 14:30 UTC. The Sun differs by 0.3″ and the Moon by 0.7″. Across 1931 to 2039 the worst planet difference is 20.3″, and a chart prints to the nearest 60″.

Result: the accuracy page names astronomy-engine and shows the per-planet table, and the PDF footer repeats the source. Score: 2.

6. Privacy

Check: does it say what it stores, who can see a shared chart, and how to delete it?

We ran: a birth form that also posted its own latitude, longitude and a UTC time zone. The server ignored them and looked the place up again by its id, so the chart used America/Chicago. That is how src/lib/birth-form.ts is written: coordinates and zone never come from the browser.

Result: the privacy page lists what is stored. A shared chart card never shows the birth date, time or place, and deleting your account removes saved charts and cards at once. The catch: charts calculated without an account are kept so their links keep working. They hold no contact details, but you can’t remove them yourself. Score: 1.

7. Birth-time handling

Check: what happens when you don’t know your birth time? A tool should drop the Rising sign and houses, not invent them.

We ran: Robin with the time blank. The chart is cast for midday (18:00 UTC), 11 placements lose their house, the Rising sign and Midheaven vanish, and a note says the Moon could be Libra or Scorpio. Leaving the time empty without ticking “I don’t know the time” is refused with this message: Add the birth time, or tick “I don't know the time”.

Result: honest handling. One gap: only the Moon gets a sign-change warning, not the Sun, which we found in our astrology calculator stress test. Score: 2.

8. Export

Check: can you keep your chart outside the tool?

We ran: the options in the code. You can save a chart to a free account and share a chart card. A printable A4 PDF (wheel, big three, every placement with its reading, up to 16 aspects and the house cusps) is built in src/lib/pdf.ts and offered only on Circle. See pricing. There is no free download, spreadsheet or data file.

Result: a good PDF, but behind a paywall, and no raw data. Score: 1.

The scorecard

That is 4 full marks, 4 half marks and no zeros. We are not claiming perfect. The four lost points come from choices, such as keeping the first chart simple, that we may revisit.

Is a free birth chart generator accurate?

On planets, a free one can match a paid one, because the astronomy is a solved problem. Tests 1, 5 and 7 are where cheap tools slip: the clock, the source and the unknown time. Price tells you nothing. The eight tests do.

Common mistakes when choosing a generator

• Judging by the wheel. A lovely graphic says nothing about whether 1974 was handled correctly.
• Trusting one tool. Run your birth through two and compare the Rising degree. A gap over a degree means a clock or house-system difference. Find out which.
• Ignoring what the tool keeps. Read the privacy copy before you type in a family member’s birth details.
• Assuming defaults are universal. Placidus and the true node are common, not the only choices.

What to do next

Pick the two or three tests you care about and run them on the tool you use now. If you’d like to see ours in action, our free birth chart generator takes a minute and needs no account. For the full method, read the accuracy page, and if a PDF matters to you, the paid Circle plan includes it.