Family Tree Calculator
Calculate family relationships from a shared ancestor, including cousins, removals, siblings, aunts, uncles, ancestors, and descendants.
Relationship calculator for genealogy and family trees
This family tree calculator compares two people by counting how many generations each person is from the same shared ancestor. It can identify siblings, cousin degree, removed relationships, direct ancestors, descendants, and aunt or uncle relationships.
A family tree calculator shows how two people are related by tracing their shared ancestor. It calculates relationships such as cousin, aunt, uncle, niece, nephew, grandparent, and removed cousin. The calculator uses each person's generation distance from the common ancestor.
Enter 0 if the person is the shared ancestor, 1 if the person is a child of the shared ancestor, 2 if the person is a grandchild, 3 if the person is a great-grandchild, and so on.
The result is relationship math, not proof of genealogy. Confirm family links with records, DNA evidence, interviews, and documented family tree sources.
Family relationship
--
Person A path
--
--
Person B path
--
--
Cousin degree
--
--
Removal
--
--
Reverse relationship
--
Shared ancestor
--
Generation gap
--
Simple tree preview
Shared ancestor
Person A path
Shared ancestor
Person B path
Note: This calculator assumes both people descend from the same named ancestor line. It does not determine biological proof, half relationships, adoption, step relationships, pedigree collapse, or multiple shared ancestors.
How to use the family tree calculator
- Find the shared ancestor: Use the closest ancestor that both people have in common.
- Count from the ancestor to Person A: A child is 1 generation, a grandchild is 2, and a great-grandchild is 3.
- Count from the same ancestor to Person B: Use the same counting method for the second person.
- Calculate the relationship: The calculator compares the two generation counts and returns the likely family relationship.
- Verify with records: Use birth, marriage, census, obituary, family Bible, DNA, or archive records to confirm the tree.
Family relationship formula
A family tree calculator uses generation distance. If two people are the same number of generations from a shared ancestor, they are usually siblings or cousins. If one person is more generations away, the difference is the number of removals.
Cousin degree is based on the smaller generation count. First cousins are grandchildren of the same ancestor, second cousins are great-grandchildren of the same ancestor, and third cousins are one generation farther down.
Cousin degree = smaller generation count - 1
Removed = difference between generation counts
Same generation + shared parent = siblings
Example: if Person A is 2 generations from the shared ancestor and Person B is 3 generations from the same ancestor, they are first cousins once removed.
Relationship references: FamilySearch cousin chart and State Library of North Carolina cousin chart.
Generation count reference
| Calculator input | Person is the ancestor's | Plain-English clue | Common mistake to avoid |
|---|---|---|---|
| 0 | Same person | The person you entered is the shared ancestor. | Do not enter 0 for both people unless they are the same ancestor. |
| 1 | Child | One step down from the shared ancestor. | Use this for siblings or aunt/uncle lines, not cousin lines. |
| 2 | Grandchild | Two steps down, often a first-cousin level. | Do not count the shared ancestor as generation 1. |
| 3 | Great-grandchild | Three steps down, often a second-cousin level. | Check whether one person is actually one generation higher. |
| 4+ | More distant descendant | Each extra step adds another generation to the line. | Longer lines need stronger source checks because names repeat often. |
Family relationship examples
| Person A generations | Person B generations | Relationship | Example ancestor |
|---|---|---|---|
| 1 | 1 | Siblings | Both are children of the same parent. |
| 2 | 2 | First cousins | Both are grandchildren of the same grandparent. |
| 2 | 3 | First cousins once removed | One grandchild and one great-grandchild of the same ancestor. |
| 3 | 3 | Second cousins | Both are great-grandchildren of the same ancestor. |
| 1 | 2 | Aunt/uncle and niece/nephew | One child and one grandchild of the same ancestor. |
Cousin chart lookup by shared ancestor
If both people are in the same generation, the shared ancestor tells you the cousin degree quickly. If one person is lower in the tree, keep the same cousin degree and add the number of removed generations.
| Closest shared ancestor | Same-generation relationship | One generation apart | Two generations apart |
|---|---|---|---|
| Parent | Siblings | Aunt/uncle and niece/nephew | Great-aunt/great-uncle line |
| Grandparent | First cousins | First cousins once removed | First cousins twice removed |
| Great-grandparent | Second cousins | Second cousins once removed | Second cousins twice removed |
| 2nd great-grandparent | Third cousins | Third cousins once removed | Third cousins twice removed |
When the calculator result may be incomplete
Real families do not always follow a single straight line. Use these checks when a relationship result looks technically correct but does not fully explain the family history.
Multiple shared ancestors
Two people can share more than one ancestral couple. Run the calculator separately for each line and record every relationship path.
Half and step relationships
A half cousin or half sibling shares only one side of a couple. A step relationship may be legally or socially important even without a biological line.
Adoption and legal family
Adoption can create a legal family relationship that differs from a biological tree. Keep legal, social, and genetic relationships clearly labeled.
DNA match vs paper tree
DNA can suggest a relationship range, while records explain the exact path. Use both carefully when names, dates, or parentage are uncertain.
What does removed mean in a family tree?
Removed means the two relatives are not in the same generation. The number of removals is the difference between their generation counts from the shared ancestor.
Same generation
First cousins, second cousins, and third cousins are not removed when both people are the same number of generations down.
Once removed
One person is one generation above or below the other, such as a first cousin and that cousin's child.
Twice removed
The relatives are two generations apart, such as a first cousin and that cousin's grandchild.
Family tree data checklist
Relationship labels are only as reliable as the tree behind them. Before you rely on a cousin or ancestor result, check whether the shared ancestor and each generation link are documented.
Names and dates
Confirm birth names, married names, nicknames, birth dates, death dates, and locations before merging people in a tree.
Source records
Look for census records, vital records, church books, immigration documents, newspapers, wills, and cemetery records.
Special cases
Half siblings, adoption, stepfamilies, unknown parents, duplicate names, and pedigree collapse can change the relationship label.
Research sources: U.S. National Archives genealogy resources, Library of Congress local history and genealogy guides, and U.S. Census Bureau genealogical resources.
Interesting fact
In a simple family tree, the number of direct ancestors doubles each generation: 2 parents, 4 grandparents, 8 great-grandparents, and 16 great-great-grandparents. In real genealogy, the tree often bends back on itself because distant relatives may share more than one ancestor. This is called pedigree collapse, and it is one reason cousin relationships can be more complex than a single calculator result.
Frequently Asked Questions
How does a family tree relationship calculator work?
It compares how far two people are from a shared ancestor in a family tree. If both people are the same generation down the lineage, the calculator usually returns sibling or cousin kinship. If one person is farther down the bloodline, the result may include removed cousin, aunt/uncle, niece/nephew, ancestor, descendant, parent, or child language.
What does first cousin once removed mean in genealogy?
First cousins share a grandparent. Once removed means the two relatives are one generation apart in the family history chart. Your first cousin's child is your first cousin once removed, and you are also that grandchild-level relative's first cousin once removed.
Are second cousins the same as cousins twice removed?
No. Second cousins are in the same generation and share a great-grandparent as their common ancestor. Twice removed means there is a two-generation gap between the relatives, such as your first cousin and your grandchild. In a pedigree diagram, cousin degree moves sideways across the chart, while removed counts move up or down generations.
Can this calculator handle half cousins, step relatives, or adoption?
It can show the basic relationship path, but it does not separately label half, step, adoptive, foster, or legal relationships. Add those details manually in your family tree notes, especially when the ancestry line, surname, household record, or legal family status differs from the biological bloodline.
What if two people share more than one ancestor?
Run the calculator once for each shared ancestor line. In some families, two people may be related in more than one way because of cousin marriages, small communities, endogamy, or pedigree collapse. A genealogy chart can show each separate lineage so the family tree does not hide a second relationship.
Is the family relationship result proof of ancestry or heritage?
No. The result is only a relationship label based on the generation counts you enter. Genealogy proof requires reliable sources, consistent records, careful identity checks, and sometimes DNA evidence. Use the calculator as a relationship guide, then support the ancestry or heritage claim with documents from your family history research.
Other useful calculators
Estimated Reading Time Calculator
Estimate reading time from text, word count and reading speed.
Golf Grip Size Calculator
Find the right golf grip size from hand measurements.
Kinetic Energy Calculator
Calculate kinetic energy from mass and velocity.
Full-Time Equivalent Calculator
Calculate FTE from employee hours and full-time schedules.
Concrete Curing Time Calculator
Estimate curing time for concrete projects and conditions.
Pool Pump Run Time Calculator
Estimate daily pool pump runtime from pool and flow data.
Family tree calculator disclaimer
This family tree calculator is for general educational, genealogy, and personal research purposes only. It is not legal advice, inheritance advice, citizenship advice, medical advice, genetic counseling, a DNA interpretation service, paternity testing, adoption advice, or proof of biological or legal relationship.
Family relationships can be affected by adoption, step relationships, half relationships, name changes, missing records, incorrect records, non-parental events, endogamy, pedigree collapse, multiple shared ancestors, and cultural naming practices. The calculator only describes the relationship implied by the generation counts you enter.
Do not rely on this calculator for estate decisions, legal family status, medical history, immigration, citizenship, tribal enrollment, benefits, inheritance, custody, or identity claims. Verify important conclusions with original records, qualified genealogists, legal professionals, medical professionals, genetic counselors, or relevant authorities.
Last updated: May 16, 2026.