How accurate are Paternity tests?

Casey Randall Alphabiolabs

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

Paternity testing is a highly accurate method of identifying whether a man is a child’s biological father. In this article we look at what can affect test accuracy and how you can be sure that your results are correct.

What is a paternity test?

A paternity test is a type of DNA relationship test that is used to verify a biological relationship between a child and their potential father.

To perform the test, DNA samples are collected from the child and any potentail fathers using cheek (buccal) swabs: a simple, pain-free method of sample collection that means the test can be performed at any time on a person of any age, including new-born babies and grown-up children/adults.

These samples can then be analyzed and compared in the laboratory to identify matching DNA markers (loci) in the DNA samples.

AlphaBiolabs examines short tandem repeat (STR) markers that are specific locations on chromosomes made up of sequences of repeated DNA. These STR markers are highly variable in length between individuals. Each individual has two copies of each STR marker, known as alleles: one is inherited from the father and the other from the mother. By looking at these specific DNA markers in each sample, it is possible to identify which half of the child’s DNA is inherited from the mother and which half is from the father.

When testing the biological father of the child, both the man and the child will share enough identical sections of DNA to confirm a biological relationship.

If the tested man is not the biological father, this will not be the case.

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How does a DNA paternity test work?

All our peace of mind paternity tests are performed in the same way, whether you want to verify paternity of an adult, or a baby who has recently been born.

Paternity testing works by comparing a child’s DNA profile with that of the potential father(s).

An AlphaBiolabs paternity test looks at up to 45 DNA markers (loci) to identify which half of the child’s DNA is inherited from the potential father.

Every person inherits half of their DNA from each of their biological parents, so such a comparison can help us to establish the probability of paternity.

When testing the biological father of the child, both will share identical sections of DNA at each marker. When the man tested is not the biological father, the man and child will not share enough DNA to verify a relationship.

What can affect the paternity test accuracy?

Our test results are 100% accurate based on the samples we receive into the laboratory. We test up to 45 DNA markers (loci), so you can be confident of getting an accurate result.

As the DNA testing kit for an ‘At-Home or Peace of mind’ paternity test will be sent directly to your specified address, you are responsible for collecting your own samples.

Our paternity test kit contains detailed, simple-to-follow instructions, which, if followed fully, will ensure you collect your samples correctly for accurate testing at our laboratory.

There is a possibility that someone may try to ‘cheat’ the test, by deliberately submitting incorrect samples. This will result in a false result.

Can a paternity test be wrong?

If the test swabs are deliberately or accidentally contaminated in any way, this will result in the need to retake the test.

When the father, mother and child participate in the paternity test, we will provide a probability of paternity in excess of 99.99% thereby confirming the biological relationship, or alternatively confirm with 100% accuracy the exclusion of the potential father.

AlphaBiolabs cannot know if the samples submitted are from the correct people and a level of trust is therefore needed between the people requesting and taking part in the test. We clearly state that the samples have not been verified and hence the report cannot be used in a court of law.

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Why does the result not show 100% probability?

A paternity test determines whether or not a tested man could have passed on his DNA to the child. A DNA test report usually include two values:

1) the Combined Paternity Index (CPI) – this provides an odds ratio of how much more likely it is that the tested man is the father rather than an untested man
2) the Probability of Paternity is based on the CPI and shows the probability that the tested man is the true biological father of the child.

These values can be calculated with or without the inclusion of the mother’s sample, but it provides even greater certainty when the mother is tested. For example, a test we completed with the mother gave a Probability of Paternity of 99.99999%; removing the mother from this test would have reduced the Probability of Paternity to 99.99%.

High probabilities of 99.99% and above are commonly seen in DNA paternity testing, but never 100%. This is because results are based on statistical calculations. A result of 100% would only be possible if AlphaBiolabs tested every male of the same ethnicity as the biological father. This is why the DNA profiling test report uses the wording ‘provides (extremely/moderately) strong support in favor of paternity’. A probability over 99% means there is relatively no chance that any other man, other than the tested man, is the father of the child.

The only exception to this is when the biological father is a close relative of the alleged father, which is why we always ask if this could be a possibility when you register your paternity test.

It is still possible to get an accurate result from paternity testing when two possible fathers are related, even if they are brothers, cousins or father & son.

Depending on the relationship, the amount of DNA shared with a relative will vary as shown in the table below:

Relationship Average % DNA shared
Identical twin 100%
Parent/child, full siblings, fraternal twin 50%
Grandparent/grandchild, aunt/uncle and niece/nephew, half siblings 25%
First cousin 12.5%<

If the two potential fathers are relatives then they will share some DNA – approximately 50% in the case of full siblings and fraternal twins. However, this also means that up to 50% of their DNA is different, which allows our expert scientists to still establish the probability of paternity. The father will share identical sections of DNA at each marker with the child, whereas the relative who is not the biological father will not share enough DNA with the child to verify a relationship.

The only situation where this is difficult is if the alleged fathers are identical twins. This is because they share near-identical DNA profiles.

You will need to tell us when ordering your test if more than one potential father is being tested and whether they are close relatives of each other.

Are home paternity tests accurate?

Yes, an AlphaBiolabs home paternity test is 100% accurate based on the samples received into the laboratory.

Our paternity test kit contains detailed, simple-to-follow instructions, which, if followed fully, will ensure your samples are collected correctly for accurate testing at the laboratory.

We have performed over ONE MILLION genetic tests since 2004, so you can be assured that our ISO 17025-accredited and award-winning testing laboratory will provide the accurate results you need.

All tests are performed assuming that a close male relative of the potential father is not the possible father. If this is not the case, you must tell us at the time of ordering the test, as it is recommended that any such relative is also tested to ensure absolute accuracy of the results.

Where can I order a paternity test online?

You can order your Home Paternity Test online for just $109 with results in 3 business days.

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Please note: our home paternity test is for peace of mind only. This means that the results are purely for your information and cannot be used for official/legal matters. If you require a legal DNA test, click here.

For confidential advice on which is the right test for you, call our friendly and discreet Customer Services team on 727-325-2902 or email

At-Home Paternity Test

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Casey Randall AlphaBiolabs

Casey Randall

Head of Genetics at AlphaBiolabs
Casey joined AlphaBiolabs in 2012 and heads up both the Genetics and Health testing teams. An expert in DNA analysis and a member of the International Society for Forensic Genetics (ISFG), Casey holds an MS degree in DNA Profiling and a BS degree 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.

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