Built for people who read charts
This is the same engine as the birth chart calculator with the prose removed. Positions to the arc minute, cusps in whichever system you pick, every aspect with its exact orb, and no interpretation in the way.
If you already read charts you want the numbers first and the explanation never. Everything here is a table.
What is in the output
Every body to the arc minute, with its sign, degree, house and retrograde status. The lunar nodes as true nodes rather than mean. Chiron, the four main asteroids and Black Moon Lilith, which most browser-based tools omit because they need a separate ephemeris.
House cusps in the system you choose. The Part of Fortune with the day or night formula applied according to the Sun's actual position, and the calculator states which it used.
The aspect list sorted by orb, with minor aspects behind a toggle so the major list stays readable. Dominants with the weights shown rather than a single asserted name.
What natal chart and birth chart mean
The same thing. Natal is the older and more technical term, from the Latin for birth; birth chart is the plain-English equivalent that took over in popular use.
Some practitioners use natal chart specifically for the untransited, unprogressed chart as cast for the moment of birth, distinguishing it from a progressed or relocated version. That distinction is real and is not a difference of definition.
House systems, and the comparison
Five are offered: Placidus, Whole Sign, Equal, Porphyry and Regiomontanus. Each is verified cusp by cusp against a reference implementation before release rather than assumed correct.
Koch and Campanus are deliberately absent. Their formulas did not reproduce the reference during testing, and shipping a house system that produces wrong cusps is worse than omitting it. If they are added it will be by porting the reference source rather than by reconstructing the formula.
| Offered | Verified against reference |
|---|---|
| Placidus | Under one arc second |
| Whole Sign | Exact |
| Equal | Under one arc second |
| Porphyry | Under one arc second |
| Regiomontanus | Under one arc second |
Orbs
Major aspects use eight degrees for conjunctions and oppositions, seven for trines and squares, five for sextiles, with two degrees added when the Sun or Moon is involved. Minor aspects use two to three degrees, and contacts involving an asteroid or a calculated point are narrowed.
Those are conventional values rather than universal ones. Adjustable orbs are not implemented yet; until they are, the orb column lets you apply your own threshold by reading rather than by filtering.
Time zone handling
Local clock time is converted using the full historical time-zone database that ships with your browser, so wartime summer time, mid-century rule changes and half-hour zones come from the record rather than from an assumption.
When a wall-clock time was skipped by a clock change or occurred twice, the result says which reading it used rather than picking one silently. That case is rare and it is where charts most often go quietly wrong.
Accuracy
Every build is compared against the Swiss Ephemeris at random dates and latitudes across two centuries before release. The planets agree to well under a third of an arc minute; the angles and house cusps to under an arc second.
The methodology page lists the figures per quantity. The places a chart can genuinely be wrong are the inputs rather than the arithmetic, and the calculator surfaces the ones it can detect.
Common questions
Is a natal chart the same as a birth chart?
Yes. Natal is the older technical term; birth chart is the plain-English equivalent. Some practitioners use natal specifically for the untransited, unprogressed version.
Why are Koch and Campanus missing?
Their formulas did not reproduce the reference implementation during testing. Shipping a house system that produces wrong cusps is worse than omitting it, and adding them means porting the reference source rather than reconstructing the formula.
What orbs do you use?
Eight degrees for conjunctions and oppositions, seven for trines and squares, five for sextiles, with two added when the Sun or Moon is involved. Minor aspects take two to three, and asteroid contacts are narrowed.
Can I change the orbs?
Not yet. Until adjustable orbs are implemented, the orb column lets you apply your own threshold by reading rather than by filtering.
How are time zones handled?
With the full historical database your browser ships. When a wall-clock time was skipped by a clock change or occurred twice, the result says which reading it used.
How accurate is it?
Planets agree with the Swiss Ephemeris to well under a third of an arc minute and the angles and cusps to under an arc second, checked across two centuries of random dates before every release.