DNA Relationship Calculator
Calculate the expected percentage of DNA shared with a relative.
From first cousins to half-siblings — understand genetic genealogy.
DNA testing services like AncestryDNA, 23andMe, and MyHeritage measure shared DNA in centimorgans (cM) or percentages. Every generation, you inherit roughly half the DNA from each parent.
Expected shared DNA by relationship:
- Identical twins: 100% (3,500 cM)
- Parent/child: 50% (1,700–1,900 cM)
- Full siblings: 50% average (2,300–2,900 cM, range due to recombination)
- Half siblings: 25% (1,100–1,500 cM)
- Grandparent/grandchild: 25% (1,300–2,300 cM)
- Aunt/uncle + niece/nephew: 25% (~1,700 cM average)
- First cousins: 12.5% (550–1,200 cM)
- Half first cousins: ~6% (~300 cM)
- First cousins once removed: 6.25% (~430 cM)
- Second cousins: 3.125% (~230 cM)
- Third cousins: ~0.78% (~48 cM)
Why ranges exist: DNA inheritance is random. Two siblings share on average 50% but can share anywhere from 38–62% due to recombination variation. Ranges widen at more distant relationships.
What centimorgans (cM) measure: Not physical distance but recombination frequency. 1 cM ≈ 1% chance of recombination per generation. The human genome is approximately 3,500 cM total.
DNA results below 90 cM could represent 3rd cousins, half 2nd cousins, or several other relationships — always cross-reference with family tree data.