What is a half-sibling?
Short answerA half-sibling is a brother or sister who shares one parent with you instead of two. Your mother’s son from another relationship is your half-brother. Half-siblings are blood relatives and share about 25% of their DNA on average, half as much as full siblings.
Half-sibling or step-sibling?
The difference is blood. A half-sibling shares one of your parents. A step-sibling is your stepparent’s child, so you share no parent at all; you are family through a marriage or partnership. If your mother marries a man who already has a daughter, she is your step-sister. If they then have a son together, he is your half-brother.
How Family Trees decides “half”
Family Trees calls two people half-siblings when each has a birth or adoptive parent the other doesn’t. A parent who simply hasn’t been entered yet is treated as unknown rather than different, so leaving a father off one child’s page never turns full siblings into half-siblings by accident.
Only siblings get the word “half”. The children of half-siblings are called first cousins in the app, as most families say; genealogists sometimes write half first cousins.
Drawing half-siblings on a tree
Give each relationship its own couple. Link the shared parent to both partners, then add each child to the right couple. The tree places half-siblings under the parent they share, with each other parent beside them, so nobody has to be left off to make the drawing work.
Let Family Trees name it for you
Every parent link in Family Trees is birth, adoptive, step or foster, and every couple is married, partners, separated or divorced. From that, the app names each relative in plain words on their page and under How are they related?, including half, step, foster and in-law relations. It’s free for up to 100 people.
Questions
Are half-siblings blood related?
Yes. Half-siblings share one biological or adoptive parent, so they are related by blood through that parent. On average they share about a quarter of their DNA.
What is the difference between a half-brother and a stepbrother?
A half-brother shares one of your parents. A stepbrother is the son of your stepparent and shares neither of your parents; you are related through your parent’s marriage or partnership, not by blood.
What are my half-sibling’s children to me?
They are your nieces and nephews, exactly as a full sibling’s children would be. Some genealogists write half-niece or half-nephew to be precise.