What this synastry calculator compares
Synastry brings two birth charts into conversation. Rather than examining only the aspects within one chart, it looks for contacts between one person's positions and another's. The calculation identifies angular relationships; astrology assigns interpretive meaning to them. That distinction matters: measuring the distance between planets does not demonstrate an effect on a relationship.
The Astral Code tool compares two birth profiles and displays their contacts and orbs. Start with your birth date and complete your profile during onboarding; then continue in My relationships within your universe. The results can help you frame shared questions, but finding answers requires listening to the people involved.
This page focuses on preparing the calculation and understanding its output. If you already have a comparison and want to work through its interpretation, continue with how to read synastry. This separates two different tasks: checking the input details and developing an interpretation in context.
Review each person's details separately
For person A, enter the date, local time and place of birth. Repeat the process for person B. Each city supplies its own coordinates and time zone: do not copy the first location if the births took place in different places. Identical recorded times can represent different moments when they belong to different time zones.
The labels A and B simply help you track where each position comes from. They do not assign emotional roles, gender or importance within the relationship. Before starting, agree on who is who and keep that reference consistent as you read. If a row mentions the Moon and Venus, you need to know which chart each planet belongs to, rather than just recognizing the names.
Check both birth times with equal care. One may be documented while the other is approximate. Do not treat them as equally reliable just to make the result look complete. If someone does not know their birth time, indicate that in their own fields. Uncertainty in one chart should not be hidden because the other has all its details.
You do not need to enter legal names, photographs or relationship details in the birth chart form. Use only the details requested and obtain the other person's consent. Sharing a birth date in conversation does not amount to permission to publish a reading about someone's private life or reuse their information in any service.
A simple way to compare your charts
Start by checking your date in your device's calendar. Continue at /es/empezar/, where you can add your birth time and place and choose what to explore. In My relationships, select the other profile or add their details with permission. Always use the recorded local time.
For the second chart, review everything from the start rather than assuming its settings match the first. If you enter coordinates manually, check the latitude, longitude and IANA time zone. Reversing a coordinate's sign can place a birth in another hemisphere. The calculation cannot guess that you meant a different city.
After submitting the form, read the result notice before going through the table. If an error appears, correct the relevant entry. Do not confuse a previous result that remains visible with a new calculation that did not finish. Keep a note of your settings if you plan to compare the result with another tool.
You can start with a few contacts rather than interpreting the whole table. Choose a specific question: how you agree on plans, express support or handle different rhythms. The comparison becomes clearer when you connect it to an experience both people can describe, without using the chart as a one-sided assessment of the other person.
How to understand the table of aspects and orbs
Each row connects a position in the first chart with one in the second. The aspect name describes an angular reference, such as conjunction, sextile, square, trine or opposition. The orb indicates how far the contact is from that exact reference. It is neither an affinity percentage nor a rating of the relationship's quality.
A conjunction refers to zero degrees of separation; an opposition to one hundred and eighty. Astrology uses other geometries between the two. The calculation allows certain margins when identifying contacts, and these can vary across programs. One table may therefore include rows another tool omits without either necessarily calculating the positions incorrectly.
| Part of the row | What to check | Reading to avoid |
|---|---|---|
| First planet | Which person it belongs to and what function it symbolizes | Attributing the entire contact to one person |
| Aspect | Which angular relationship is being identified | Automatically classifying it as good or bad |
| Second planet | What function comes into relation from the other chart | Assuming it means the same thing as the first |
| Orb | Distance from the exact reference being used | Turning a small number into a guarantee of connection |
| No rows | If contacts are missing within settings | Concluding there is no real affinity |
The total number of aspects does not determine how much two people love each other, either. A long list may reflect the number of bodies included and the selected orbs. Before comparing counts or apparent intensity, confirm that both calculations use similar criteria. The technical settings help explain the result.
What can you explore when there is an hour left?
An unknown birth time prevents you from establishing that chart's angles and houses reliably. It also means treating the Moon's position as a reference that may change throughout the day. A form accepting a date does not mean every layer of interpretation has the same precision.
Some comparisons between slower-moving planets may remain useful as an approximation for the day, but even a contact close to the orb limit calls for caution. The table shows the calculation performed; it does not certify that every row stays the same throughout the possible time range. Keep the uncertainty notice alongside any conclusions you draw.
If you know only one birth time, do not invent the other to produce a symmetrical result. A partial comparison can support a conversation about general themes, provided you do not add assumed houses or Ascendants. The guide to an unknown birth time explains why leaving a detail open is part of a responsible reading.
When you find a more reliable record, you can calculate again. The new result may change degrees, contacts or information that was previously unavailable. This does not mean the relationship changed at that moment: the precision of the details describing the two births has changed.
An example: discussing support without passing judgment
Imagine a row connecting A's Moon with B's Mercury. As a symbolic exercise, you can explore how needs for care meet ways of communicating. The table does not tell you which conversation took place or who was right. An opening question might be: when one person needs company, does the other offer listening, explanations or practical solutions?
Suppose A recognizes that sometimes they want to be heard, while B tends to suggest alternatives immediately. That observation comes from their experience; the aspect does not prove it. They could agree on a simple question before responding: “Would you like me to listen, or shall we think through some options?” The value lies in a practical agreement both can try.
Now look for a situation that challenges the first example. Perhaps in another context A wants a concrete answer and B needs time to work out what they think. That difference keeps them from becoming fixed characters. Symbolism should not erase changes in circumstances, tiredness, learning or preferences that a chart cannot contain.
The same caution applies to Venus–Mars or Sun–Saturn contacts. They do not justify claims that someone feels desire, that a relationship will last or that there is an obligation to stay together. A reading can suggest themes; it never replaces consent, respect or what each person says about their own experience.
Synastry, zodiac sign compatibility and composite charts
A compatibility by signs works with a broad layer of zodiac symbolism. It can be an accessible introduction, but it does not compare all the planets of two births on its own. Synastry uses positions from both charts to distinguish specific contacts. The same pair of Sun signs can occur in relationships with very different birth chart configurations.
A composite chart uses a different procedure: it builds positions from the midpoints between the two charts. It is not simply synastry drawn differently. Its results should therefore not be combined without explaining which method is being used. This public calculator focuses on comparing aspects between charts, rather than providing a composite chart in the same output.
If you are just starting out, first review each birth chart individually. Understanding the positions separately helps you avoid attributing an entire personal function to an encounter with someone else. You can then return to the comparison and ask what the contact adds, rather than treating every row as a complete explanation of the relationship.
Can also be used outside of a pair
An astrological comparison can involve friends, relatives or people working on a project together, provided there is agreement and clear expectations. Not every contact needs to be interpreted as romantic attraction. In a collaboration, for example, it may be useful to discuss organization and ways of exchanging ideas without assigning work roles by zodiac sign.
In a friendship, the question might be how to respect different rhythms when arranging to meet. The result cannot decide who is more loyal or who should give way. Describe observable behavior, express preferences and revisit agreements. Synastry should not be used to select staff, exclude people from a group or justify unequal treatment.
If a reading causes fear or pressure to stay in a relationship you do not want, stop using it as a basis for decisions. No aspect makes abuse a necessary lesson or obliges anyone to tolerate harmful behavior. Personal boundaries and safety take priority over any symbolic interpretation.
Frequently asked questions about free synastry
Does the result include a compatibility percentage?
This tool presents a summary and aspects, rather than a probability of relationship success. A decorative number could not measure agreements, shared values or the ability to resolve conflict. Read each contact as a possible topic for conversation and avoid turning the comparison into a competition between relationships.
What changes if I swap person A and person B?
The angular distance between two positions stays the same when you reverse the order, but you must still track which planet belongs to whom. A's Moon with B's Venus is not the same pair as A's Venus with B's Moon. Techniques involving house overlays also require attention to the direction of the comparison.
Does a square mean the relationship will fail?
No. One isolated contact does not describe an entire relationship or measure people's real ability to communicate or set boundaries. Look at what happens between you before assigning meaning to the geometry.
Why do I see other aspects on a different website?
Compare birth data, zodiac, included bodies and supported orbs. One tool may list minor aspects that another does not use. If there is also an hour missing, check what time reference each one took. Save the configuration so you can explain the discrepancy and refer to the methodology when you need to understand the calculation's limits.
Can I save or share the other person's details?
Only with their permission and through an option whose scope you both understand. Viewing a comparison does not authorize publishing complete birth details. Review the privacy notices and avoid screenshots that unnecessarily expose dates, times or places. You can discuss a conclusion without sharing the entire form.
How can I go deeper without interpreting everything at once?
Choose a row and follow the guide reading synastry. Identify the planets first, then the aspect, and finally a real situation both people want to discuss. If the reading does not bring clarity, you can set it aside. An exploratory tool does not have to answer every question about a relationship.