Free Synastry Calculator With Aspects
Selected planetary contacts · Orbs · No sign-up
Compare two birth charts for a free synastry aspect list with named contacts, measured orbs and a preview score. Enter both birth dates and places, adding recorded times when known. No sign-up is required for this preview. You can leave either birth time blank; that person’s chart uses a local-noon estimate, so Moon contacts and the score remain provisional.
Using the synastry calculator without birth times
You can compare selected planetary contacts when one or both birth times are missing. Leave an unknown time blank instead of entering a guessed morning or evening time. The calculator uses noon in that birthplace’s time zone as an estimate, not as a recovered birth time. Keep the recorded time for the other person when you have it.
A noon chart gives one set of planetary positions. It does not check every possible position across the birth day. The Moon can move enough to change a sign or bring a contact into or out of an allowed orb; other near-boundary contacts can change too. Treat those rows and the preview score as provisional. This aspect-list preview does not provide house overlays or Ascendant contacts, even when both times are known.
How to Compare Two Birth Charts
Run a free synastry comparison between two birth charts.
- 1. Enter the first person's birth date and place; add a recorded time or leave the time blank
- 2. Enter the second person's birth details
- 3. Read the selected cross-chart contacts, named aspects and measured orbs, sorted with the tightest first
Related guides
More compatibility tools
Continue on Natal Echo
FAQ
What is synastry?
Synastry compares positions from two birth charts. For example, the first person’s Moon can form an aspect to the second person’s Mercury. The result identifies the two bodies, the aspect and its orb, so you can tell which contact an interpretation is discussing.
How is the preview score calculated?
The preview scores up to twelve of the tightest selected contacts, weighted by aspect type and closeness to exact. The aspect counts can include more contacts than the score uses. A smaller orb means the measured angle is closer to the named aspect; it does not measure the likelihood of relationship success.
Does the preview score predict relationship success?
No. It summarizes selected contacts and weights in this preview. A number cannot establish feelings, safety, consent or a future outcome. Compare the actual contacts and method, and keep the result separate from the people’s decisions.
What does this free synastry calculator include?
The preview compares the first chart’s Sun, Moon, Mercury, Venus and Mars with the second chart’s Sun through Saturn. It lists qualifying cross-chart contacts and orbs. It is a focused preview, not every possible body, a complete house-overlay report or a written relationship consultation.
Why can another synastry calculator list different aspects?
This preview measures true angular separation using planetary longitude and latitude. It allows 8° for conjunctions, 4° for sextiles, 6° for squares and trines, and 7° for oppositions. Other tools can choose different bodies, orbs or longitude-only angles. Those are method differences, not proof that one relationship score is correct.
Do I need to pay or sign in for the written report?
No sign-in is needed for the aspect preview. The full written comparison is on the compatibility page, requires sign-in and uses the account’s current free or paid allowance. Check that page before generating a reading.
How do I read a contact with a 2° orb?
For a simple illustration, put one person’s Moon at 15° and the other person’s Mercury at 17°, both at zero latitude. They are 2° apart, so the preview lists a conjunction with a 2° orb. Real results use both longitude and latitude. An orb measures the difference from the aspect’s exact angle; it is not a strength rating for the people’s feelings.
Will swapping person A and person B change the preview?
It can. This preview compares person A’s Sun through Mars with person B’s Sun through Saturn. Swapping the people changes which Jupiter and Saturn contacts are included, even though the underlying angle between any fixed pair of positions is unchanged. Keep the person labels consistent when comparing two runs.
Can I calculate synastry if only one birth time is known?
Yes. Enter the known time and leave the other person’s time blank. Only the missing time is replaced with a local-noon estimate. Read contacts involving that person’s Moon with particular care. A recorded time for one person does not establish the other person’s Ascendant or houses; this preview shows selected planet-to-planet contacts rather than house overlays.
Can a missing birth time change the synastry score?
Yes. Changing an estimated time can change planetary positions, especially the Moon, which can change the qualifying contacts, their orbs and which twelve contacts contribute to the score. The score is a summary of this calculation, not a relationship-success percentage. A precise-looking number does not remove uncertainty in the input.