This calculator and content are verified for alignment with modern synastry principles.
Use the Birth Chart Compatibility Score Calculator to quickly determine the weighted potential between two individuals based on key planetary aspects in their natal charts (Synastry). This tool averages the scores you assign to the Sun, Moon, Venus, and Mars connections.
Birth Chart Compatibility Score Calculator
Calculated Compatibility Score:
0.00%Detailed Steps will appear here after calculation.
Birth Chart Compatibility Formula
We use a weighted average based on the significance of each planetary aspect in synastry:
Compatibility Score (%) = $\left(\frac{(S \times 3) + (M \times 4) + (V \times 5) + (R \times 2)}{14}\right) \times 10$
Formula Source Reference:
Astro.com – Synastry Basics,
Cafe Astrology – Relationship Astrology
Variables
- S (Sun Compatibility Score): Your score (1-10) for the compatibility of core identity and ego. Weight: 3.
- M (Moon Compatibility Score): Your score (1-10) for emotional rapport and inner needs. Weight: 4.
- V (Venus Compatibility Score): Your score (1-10) for affection, harmony, and relationship values. Weight: 5 (Highest weighting for relationship focus).
- R (Mars Compatibility Score): Your score (1-10) for passion, action, and motivation/drive. Weight: 2.
- 14 (Total Weight): The sum of all weights ($3+4+5+2$).
Related Calculators
What is Birth Chart Compatibility (Synastry)?
Birth chart compatibility, or Synastry, is the astrological technique of comparing two natal charts to determine the nature and dynamics of a relationship. It involves examining the planetary relationships (aspects) between the charts, which reveal areas of harmony, challenge, attraction, and friction. It is a nuanced tool used to understand interpersonal dynamics beyond simple Sun Sign comparisons.
The compatibility score is a simplification of a complex process, designed to give an overall indication. The Moon (emotions and comfort) and Venus (love and attraction) are often weighted more heavily than the Sun (ego) and Mars (sex and action) for long-term relational harmony, which is why they carry higher multipliers in this specific formula.
How to Calculate Birth Chart Compatibility (Example)
Let’s calculate the score using the example default inputs: S=8, M=9, V=7, R=6.
- Step 1: Apply weights to each score.
- Sun: $8 \times 3 = 24$
- Moon: $9 \times 4 = 36$
- Venus: $7 \times 5 = 35$
- Mars: $6 \times 2 = 12$
- Step 2: Calculate the Total Weighted Score. $$ \text{Total} = 24 + 36 + 35 + 12 = 107 $$
- Step 3: Divide the Total Weighted Score by the Total Weight (14). $$ \text{Average Score} = 107 / 14 \approx 7.6429 $$
- Step 4: Convert the Average Score (out of 10) to a Percentage (out of 100). $$ \text{Compatibility Score} = 7.6429 \times 10 \approx 76.43\% $$
Frequently Asked Questions (FAQ)
What is the most important factor in Synastry?
The aspects involving the Moon and Venus are generally considered the most critical for emotional and relational satisfaction, as they govern comfort, affection, and love. The Venus score has the highest weight in this calculator for that reason.
Can a low compatibility score be overcome?
Yes. Astrology suggests tendencies, not destiny. A low numerical score indicates more areas of tension (e.g., challenging Mars aspects), but conscious effort, communication, and free will can always overcome natal challenges.
Is a score of 100% possible?
A score of 100% is theoretically possible if all input scores are 10, indicating perfect alignment on all four key areas. However, this is extremely rare in real-world synastry analysis.
Why are outer planets (Jupiter, Saturn, etc.) not included?
Outer planets are often included in deep analysis, but they primarily affect generational themes and major life structure. For a quick relational compatibility score focused on personal dynamic, the inner planets (Sun, Moon, Venus, Mars) are prioritized.