Start with this tool
Calculate synastry using two saved birth charts. Compare planetary aspects, orbs and mutual house overlays, including the Sun, Moon, Venus and Mars.
First create and save astrology birth charts for the two people you want to compare. Select both charts from the lists here to calculate aspects between actual planetary degrees and mutual house overlays. Use the Sun-sign tool for a quick comparison of two signs, or the love-compatibility guides to read about a particular sign pair.
Calculation and interpretation method
The first person's planets are compared with the second person's planets. House overlays are calculated separately in both directions; each person's own cusps are retained even if their house systems differ. The tool does not calculate a success percentage, a soulmate guarantee or a relationship outcome.
Discuss one shared need
Choose one Moon, Venus or Mars contact across the two charts. Read whose degrees are being compared and the aspect's orb. Turn it into a question about contact, space or time needed for closeness. Let each person provide an example separately. Rather than treating a similar symbol as proof of identical needs, use the conversation to learn where experiences overlap and which details remain different.
Track the first-to-second and second-to-first direction when reading house overlays. The same aspect can enter different house contexts for each person. Ending with one need and a trial agreement offers a more concrete result than judging the entire relationship through one sign.
Retain both directions and both people's experience
Synastry compares actual longitudes across two charts. One person's planet in the other's house is a different calculation from the reverse overlay; each chart retains its birth time and house system. A placement's theme does not reveal another person's intention. Choose a conversation or shared experiment both people actually accept. The same aspect can be experienced differently in different circumstances. Angular separation does not produce a relationship-success percentage or guarantee of working well together.
Sources and approach
These sources explain the page's traditional concepts or calculation context. Original Starmora examples and reflection prompts are not predictions attributed to the sources.