Can a DNA test prove half-siblings?

Casey Randall AlphaBiolabs

By Casey Randall, Head of Genetics at AlphaBiolabs
Last reviewed: 11/10/2023

In this article, we discuss DNA testing for siblings, and whether a DNA test can prove half-siblings.

What is sibling DNA testing?

A sibling DNA test is a type of DNA test that is used to determine whether two or more individuals are full siblings or half siblings.

For a sibling DNA test, cheek swabs are used to collect DNA samples from each sibling. For the most conclusive result, the laboratory will also request that the biological mother’s DNA sample be submitted for testing, if possible.

Expert geneticists will then analyse and compare the DNA samples to determine the genetic profile of the possible siblings and calculate a sibling DNA index or likelihood ratio.

  • A likelihood of greater than 10 supports that the tested individuals are likely to be related
  • A likelihood of less than 0.1 is not supportive, meaning the individuals are unlikely to be related
  • A likelihood which falls between 0.1 and 10 is considered inconclusive, which means a relationship cannot be determined based on the statistical probability obtained from the analysis

How much DNA do half-siblings share?

Half siblings share approximately 25% of their DNA, inheriting DNA in common from their shared parent (mother or father).

Male half-siblings who have the same biological father will have the same Y chromosome. This is because all male children inherit their Y chromosome from their father.

Can a sibling DNA test prove half-siblings?

Yes, a sibling DNA test can be used to prove whether individuals are half-siblings.

Half siblings share one biological parent – the mother or father – and will normally share more DNA than people who are not related.

This means that it is possible to use sibling DNA testing to determine whether individuals are:

  • more likely to share one common parent i.e. they are half siblings, with one biological parent (mother or father) in common, or
  • are more likely to be unrelated

Where can I buy a sibling DNA test?

It’s easy to order your peace of mind Sibling DNA Test online now for just €229, with results in 2-3 working days.

Simply place your order online and we will ship your test kit out to you in discreet, plain packaging, for full confidentiality.

Your home test kit will contain everything you need to collect your samples and return them to our ISO 17025-accredited laboratory for analysis by our in-house geneticists.

For confidential advice on whether this test is right for you, call our friendly and discreet Customer Services team on 01 402 9466 or email

Home Sibling DNA Test

Order our Sibling DNA Test online now for €229.

Casey Randall AlphaBiolabs

Casey Randall

Head of Genetics at AlphaBiolabs

Casey joined the AlphaBiolabs team in 2012 and heads up the DNA laboratory.

An expert in DNA analysis and a member of the International Society for Forensic Genetics (ISFG), Casey holds an MSc with Distinction in DNA Profiling and a First-Class BSc with Honours in Forensic Science.

Casey is responsible for maintaining the highest quality testing standards, as well as looking for ways to further enhance the service that AlphaBiolabs provides and exploring new and innovative techniques in DNA analysis.

Related articles…