DNA Sharing Calculator

What is DNA Sharing?

DNA sharing refers to the percentage of genetic material that two individuals inherit from a common ancestor. Humans share approximately 99.9% of their DNA with all other humans, but the small differences are what make us unique. When we talk about DNA sharing in genealogy, we're referring to segments of DNA inherited from recent common ancestors.

What are centiMorgans (cM)?

A centiMorgan (cM) is a unit used to measure genetic linkage. It represents the distance between chromosome positions and indicates the likelihood that two DNA segments will be inherited together. In DNA testing:

• Higher cM values indicate closer relationships (e.g., parent-child: ~3,400-3,700 cM)
• Lower cM values indicate more distant relationships (e.g., third cousins: ~0-230 cM)
• The total human genome is approximately 7,000 cM
• You inherit about 3,500 cM from each parent

How DNA is Inherited

DNA inheritance follows these principles:

• You inherit 50% from each parent - This is the only relationship with exact DNA sharing
• Genetic recombination creates variety - Siblings can share between 38-61% DNA despite having the same parents
• DNA halves with each generation - Grandparents (25%), great-grandparents (12.5%), etc.
• Distant relatives may share no DNA - Third cousins and beyond might not share detectable DNA segments

Why Ranges Exist

Except for parent-child relationships, DNA sharing has a range because of genetic recombination during meiosis (cell division). When gametes (sperm and egg cells) form, chromosomes swap segments randomly. This means siblings, for example, don't inherit identical DNA from their parents, leading to the 38-61% variation.