Compare two siblings' birthdays for a score written around rivalry, loyalty and shared history rather than romance.
Enter two birthdays and a relationship type to get an easy-to-read compatibility report with printable details.
Siblings are the longest relationship most people will ever have. It outlasts the parents and usually predates the partner. It is also the only close bond that begins in direct competition - for attention, for space, for the version of family history that gets told at the table.
That competition is why the sibling score carries its own modifier. Brothers and sisters absorb far more friction than friends do without the relationship breaking, because the exit does not exist. A sibling pair scoring in the sixties is not a warning; it is an ordinary, functional, occasionally loud family relationship.
What the sign pairing tends to expose is the division of labour siblings fall into without ever agreeing to it. One becomes the organiser, one the peacemaker, one the one who says the thing everybody is thinking. Fire and air pairings often argue openly and recover quickly. Earth and water pairings tend to avoid the confrontation and carry it for longer. Neither is healthier - they simply fail differently.
Read the challenges section with adult siblings in mind, not children. Sibling friction rarely stays about what it was about. It resurfaces around weddings, around a parent's illness, around who visits and who does not, around money. Knowing that your brother needs the decision made and you need the decision discussed is worth more at those moments than at any point in childhood.
If there are three or more of you, run each pair. The pattern that emerges - which two are the easy pair, which one sits between the other two - is usually recognised instantly by everybody in the family.
Each relationship type is scored differently, because each one carries a different amount of shared history.
Why you and your mother-in-law read each other so differently
How your sign and your child's sign actually meet
What passes down between two generations that skipped one
Family by default, friends by choice
The chemistry that has nothing to do with romance
Two birthdays, one honest look at the pairing
The calculator uses a local zodiac engine and deterministic compatibility rules so the same dates always produce the same report.
Yes. The calculation uses two birth dates and the sibling relationship type. It makes no assumption about shared parents.
Siblings carry a positive modifier and in-laws a negative one. Shared history absorbs friction that a relationship with no history cannot; the calculator reflects that difference deliberately.
Twins usually share a sign, which the calculator handles - same-sign pairings score highly on natural understanding and are often the pairings where the challenges section is the more useful half.
Use the family zodiac chart, which takes several birthdays together and shows the whole sign spread plus the strongest and most-strained pairings in one view.
One chart for the whole family - every sign, the dominant element, and the pairings at either end.
Explore family and kinship connections in a simple format.
Create a polished family tree with guided prompts.
Turn your family history into a beautiful timeline.