Your birth details
Use your date, exact time, and birth location for the first chart.
Synastry
Synastry Calculator
Learn how synastry compares two birth charts for love, communication, chemistry, and long-term fit. Your personal two-chart result is available in the paid Cosmic app.
Last updated: 2026-08-21
Compare Our Charts
Their birth details
Use the second person's date, exact time, and location for the clearest synastry reading.
Two complete charts
Synastry works best when both charts are precise, especially for Moon, Rising, and house overlays.
How the synastry calculator works
1
Calculate both natal charts
The app creates a full chart for each person using exact birth data.
2
Compare planets, signs, and houses
Synastry overlays the two charts to show attraction, tension, ease, and growth themes.
3
Read the relationship pattern
You see how Sun, Moon, Venus, Mars, angles, and house overlays shape the connection.
What the synastry calculator shows
Emotional compatibility
Moon contacts show how the relationship feels and where each person needs care, closeness, or space.
Attraction and chemistry
Venus and Mars contacts show affection style, magnetism, and how desire moves between two people.
Long-term dynamics
Angles, Saturn contacts, and house overlays reveal staying power, lessons, and growth themes.
Chart math first. Interpretation second.
VSOP87 Ephemeris
Trusted astronomy model for stable planet positions
10 House Systems
Choose the house system that fits your practice
See Your Chart
See the transits and chart context behind the guidance
Plainly worded
Designed for specific, non-fear-based daily guidance
Synastry calculator FAQ
What is synastry?
Synastry is the astrological technique of comparing two birth charts to understand how the relationship flows, where there is chemistry, and where extra work may be needed.
Do I need both birth times?
Yes, if you want the most reliable synastry reading. Exact times improve Moon, Rising, angle, and house-overlay accuracy.
How is synastry different from Sun sign compatibility?
Sun sign compatibility compares only one placement. Synastry compares the full two-chart relationship, including Moon, Venus, Mars, aspects, and house overlays.
Can a synastry calculator predict soulmates?
No chart can guarantee outcomes. Synastry helps you understand patterns, attraction, friction, and growth, but communication and real choices still matter.
What if one birth time is unknown?
You can still get directional insights, but the reading will be less precise around house overlays, the Ascendant, and timing-sensitive placements.
Related guides
Ready to compare both charts?
Generate two charts and see your synastry profile for attraction, communication, emotional fit, and long-term potential.
Compare Our Charts