⊻ Free Vertex Calculator · The Third Angle
Umbriel's free Vertex calculator finds your Vertex and Anti-Vertex (sign, exact degree and house) from your birth date, time and place.
No account, no email. The Vertex depends on the latitude you were born at as much as the time, which is why it behaves strangely for births far from the equator.
- What you'll needBirth date, exact time and place
- What you getYour Vertex and Anti-Vertex, with sign, exact degree and house
- CostFree, no account required
What the Vertex is
The Vertex is a third angle, less famous than the Ascendant and Midheaven and calculated differently: it is where the prime vertical (the great circle running due east, overhead and due west) meets the ecliptic in the western half of the sky. The Anti-Vertex is the point opposite. It is a real piece of geometry, not an interpretation, but it is a modern addition to practice.
It is unusually sensitive to where you were born. Because the prime vertical tilts with latitude, the Vertex is not simply a function of the clock: two people born at the same instant at different latitudes get very different Vertexes, and at extreme latitudes the geometry becomes unstable enough that the point is of doubtful use. For most inhabited latitudes it is well behaved, and Umbriel calculates it from your actual coordinates, not a rounded city centre.
It is conventionally read as a point of encounter: meetings that arrive from outside rather than being sought, which is why it turns up most often in synastry, where someone else's planet falling on your Vertex is treated as significant. That reading is modern and not universally accepted, and it is worth holding lightly. The geometry is exact; the meaning attached to it is a convention roughly as old as Chiron's.
How Umbriel computes it
The Vertex is a point on the ecliptic that Umbriel computes from your birth moment and birthplace, and it is not a planet. It is the Ascendant formula run again for the co-latitude of your birthplace (90 degrees minus the absolute value of the latitude), using the local sidereal time turned half a circle and the obliquity of the ecliptic for your birth date. The result is a longitude, from which the sign, degree and house are read like any other point, and the house comes from the cusps of your chosen house system. The Vertex needs your exact birth time and place, because it comes from the sidereal time at the birthplace, and Umbriel computes no Vertex and no houses for a chart with no birth time. The Ascendant moves about 361 degrees a day, so the Vertex swings quickly through the zodiac and a few minutes of error in the birth time moves it. In a sidereal chart the ayanamsa is subtracted from its longitude. The accuracy page states the Ascendant and Midheaven as within 0.5 arcminutes of an independent implementation, and the Vertex is built from the same sidereal time. The Vertex is also not calculated on a chart cast with the extra points switched off.
What's in your result
- Vertex sign and exact degreeTo the degree and minute, calculated from your birth coordinates.
- The Anti-VertexThe opposite point, given explicitly.
- The house it falls inUsually the 5th to the 8th for mid-latitude births, which is a property of the geometry, not a coincidence.
- Aspects to the VertexContacts with exact orbs.
- In synastryWhere another person's planets fall against your Vertex, which is where the point is most used.
- Alongside the other anglesAscendant, Midheaven and Vertex together, so you can see all three.
Don’t know your birth time?
Know it roughly? Give the time and say where it came from (a certificate, a parent’s memory, or something rough like “early morning”), and your chart tells you what could change within that window.
Don’t know it at all? Umbriel does not fill the gap with a guess. Tick “I don’t know the time at all” and it checks your whole birthday, hour by hour, then tells you two things: which placements are the same whatever time you were born, as exact as they would be if you knew the minute, and which are down to two signs, both named, so you know what a parent’s memory would settle.
The Ascendant, the Midheaven and the houses are left out rather than approximated. A birth time is the one thing they cannot be computed without, and an approximate Rising sign that looks exact is worse than no Rising sign at all.
Common questions
What is the Vertex in astrology?
The point where the prime vertical (the circle running due east, overhead and due west) crosses the ecliptic in the western sky. It is sometimes called a third angle, and is usually read as a point of encounter.
Do I need a birth time for the Vertex?
Yes, and an accurate one. The Vertex depends on both the exact time and the latitude of birth, and it moves quickly. Without a birth time there is nothing to calculate.
Why is my Vertex always in the 5th to 8th house?
That is the geometry, not a coincidence. For most inhabited latitudes the Vertex falls in the western half of the chart, and it lands in that range for the great majority of births. It is not a special feature of your chart.
Is the Vertex reliable at high latitudes?
Less so. The prime vertical's tilt increases with latitude and the calculation becomes unstable towards the poles, so a Vertex from a far-northern or far-southern birth deserves more caution than one from a mid-latitude birth.
Is the Vertex calculator free?
Yes. Vertex, Anti-Vertex, house and aspects, with no account and no email.
What if I don’t know my birth time?
Umbriel checks your whole birthday hour by hour and separates what is certain from what is not. Placements that are the same whatever time you were born are shown as exact. Placements that changed sign during the day are shown as two named signs, so you know what a parent's memory would settle. The Ascendant, Midheaven and houses are left out rather than approximated. They cannot be computed without a time, and an approximate Rising sign that looks exact is worse than none.
Do I need an account or an email address?
No. There is no sign-up, no email capture and no free trial. Enter your details and the result is drawn in your own browser.
Go deeper
Every one of these is a page in its own right, written out one at a time.
Related free tools
Umbriel offers every system here as a set of prompts to think with, never as a statement of fact about who you are. Take what's useful, leave the rest.