How to Read Paternity Test Results: Understanding Your DNA Report

You have your paternity test results in hand. Maybe you pulled them up on a secure online portal, or maybe a printed report showed up in the mail. Either way, the page in front of you is full of numbers, percentages, and scientific terms that probably do not make much sense yet.

That is expected. DNA reports are written for labs, courts, and medical professionals. They are not written for someone reading one for the first time. But once you know what each section means, the whole report is pretty simple to follow. Below is your paternity test results explained in plain language, section by section, so you can understand exactly what your report is telling you.

What Do Paternity Test Results Look Like?

Before getting into the numbers, it helps to know what a report looks like overall. A standard paternity test report has five main sections, and nearly every accredited lab follows the same general layout.

Participant Information

At the top, you will see identifying details for each person tested: name, date of birth, date of sample collection, and a case number or specimen ID. Legal tests may also include a photo ID reference and the name of the collection witness. This section confirms whose DNA was analyzed. Always double-check that the names and details are correct.

Genetic Marker Table

The biggest section of the report is a table listing the genetic markers that were tested. This is the raw data behind the conclusion, and it is where most people get confused. Each row is a different genetic marker location. The columns show the allele values found for each participant. More on this below.

Combined Paternity Index (CPI)

Below the marker table, you will find a single number called the Combined Paternity Index. It tells you how many times more likely it is that the tested man is the biological father compared to a random, unrelated man from the general population.

Probability of Paternity

Next to or just below the CPI, there is a percentage. This is the probability of paternity, and it is the number most people look at first. A result of 99.99% or higher confirms paternity. A result of 0% rules it out.

Conclusion Statement

At the bottom of the report, the lab provides a written conclusion. It will say either the tested man "is not excluded as the biological father" or "is excluded as the biological father." The wording is formal, but this is the final answer.

Understanding the Genetic Marker Table

The genetic marker table is the core of the report. Once you understand how it works, the rest falls into place.

Each row represents a specific location on a chromosome, called a locus. Think of it as a fixed address on your DNA that scientists check every time. The table has a column for the locus name, which shows up as a code like D3S1358, D21S11, or TH01. You do not need to know what those mean. They are just standardized labels for which part of the DNA was examined.

Next to each locus name, you will see columns with allele values for the child, the alleged father, and sometimes the mother if she was tested. Alleles show up as numbers like 14, 16, or 18. Every person has two alleles at each locus, one from each biological parent. So each person's column will have two numbers per row.

Here is how you actually read it: at every locus, at least one of the child's two allele numbers should match one of the alleged father's numbers. A biological child inherits one allele from the father at each location. If you go down the table and see consistent matches at every marker, that is strong evidence of a biological relationship.

Most accredited labs test 20 or more genetic markers. US Diagnostics Center tests up to 28 genetic markers, which gives more statistical weight to the final result. More markers means more data points backing up the conclusion. If you want to understand the broader science behind this process, the guide on how DNA testing works covers the full step-by-step lab procedure.

What If a Single Marker Does Not Match?

One or two non-matching markers does not automatically mean the tested man is excluded. Genetic mutations can cause a single marker to look different even when the man is the biological father. Labs account for this by looking at the overall pattern across all markers, not just one. If mutations are suspected, the lab applies a mutation rate calculation and adjusts the final probability. But if three or more markers do not match, the tested man is excluded with certainty.

What the Combined Paternity Index Means

The Combined Paternity Index, or CPI, is a number that represents the weight of all the genetic evidence together. It answers one question: how many times more likely is it that this man is the father, compared to a random unrelated man?

The lab calculates a paternity index for each locus in the marker table. Those individual values are multiplied together to get the CPI. Testing more markers leads to a higher and more reliable CPI because each additional matching marker multiplies the overall strength of the evidence.

For example, a CPI of 100,000 means the tested man is 100,000 times more likely to be the biological father than a random man. A CPI of 1,000,000 means he is one million times more likely. In confirmed paternity cases, the CPI is usually in the hundreds of thousands or millions.

A higher CPI means stronger evidence. There is no specific CPI cutoff that confirms paternity by itself, but the CPI feeds directly into the probability of paternity percentage, which is the number most people and courts rely on.

When someone is excluded, the CPI will be 0. The allele mismatches at multiple markers make it statistically impossible for the tested man to be the father.

Probability of Paternity: What the Percentage Means

The probability of paternity is the clearest number on the report. It is calculated from the CPI using a standard statistical formula, and it expresses the likelihood that the tested man is the biological father as a percentage.

Here is how to read it:

• 99.99% or higher means the tested man is "not excluded" as the biological father. In plain terms, he is the biological father.
• 0% means the tested man is "excluded" as the biological father. He is not the father.

You will notice the number never hits exactly 100%. That is a statistical convention, not a sign of uncertainty. DNA testing works with probabilities, so the math always produces a number just under 100%. Any result at or above 99% is considered conclusive by labs, courts, and government agencies worldwide.

In most confirmed cases, the probability is 99.9999% or higher, depending on how many markers were tested and the CPI. There is no real difference between 99.99% and 99.9999%. Both confirm paternity.

Inclusion vs. Exclusion: The Two Possible Outcomes

Paternity test results have two possible conclusions. There is no middle ground when the test is properly completed.

Not Excluded (Inclusion)

If the report says the tested man "is not excluded as the biological father," the DNA confirms he is the father. The probability of paternity will be 99.99% or higher, and the CPI will be a large number, usually in the hundreds of thousands or millions. People commonly call this a "positive" paternity test result.

If you got this result and want to know what to do next, including legal steps and practical guidance, the article on what a positive paternity test means and what to do next covers that.

Excluded (Exclusion)

If the report says the tested man "is excluded as the biological father," the DNA rules him out. The probability of paternity will be 0%, and the marker table will show mismatches at multiple loci. Unlike inclusion, which is expressed as a high probability, exclusion is absolute. There is no ambiguity.

One thing to be aware of: if the alleged father has an identical twin, a standard paternity test cannot tell the two men apart because identical twins share nearly the same DNA. This does not come up often, but if it applies to your situation, the article on whether identical twins have the same DNA explains the science.

What to Do If Your Results Are Inconclusive

Occasionally, a paternity test comes back inconclusive instead of giving a clear inclusion or exclusion. This does not mean the test failed. It means the lab did not have enough data to reach a definitive answer with the samples provided.

The most common reason is that the mother's DNA was not included. When only the alleged father and child are tested, the lab has to figure out which of the child's alleles came from the mother and which came from the father. Usually that works fine, but sometimes the genetic profiles make it hard to sort out without the mother's data. Adding her sample almost always clears it up, and most labs will process the extra sample at no additional charge.

Poor sample quality is another reason. If the cheek swabs were not collected properly, if the person ate or drank right before collection, or if the samples sat in heat or moisture during shipping, the DNA may be degraded. When that happens, the lab will typically send a new kit for recollection at no charge.

An inconclusive result is not a final answer. It just means the lab needs more information. If you got one, contact your testing provider to find out the specific reason and what will fix it. You can also check the FAQ page for answers to other common testing questions.

Tips for Reviewing Your Report

Once you know the structure, reviewing a paternity test report comes down to a few things.

• Verify participant information. Make sure the names, dates of birth, and case numbers are correct. Errors here could mean a mix-up, which almost never happens but is worth checking.
• Look at the probability of paternity first. That single number gives you the answer. 99.99% or higher means paternity is confirmed. 0% means the tested man is excluded.
• Check the number of markers tested. More markers mean a stronger result. Industry standard is 20 or more, and you should see at least that many rows in the genetic marker table.
• Read the conclusion statement. This is the lab's official determination in plain language. It should line up with the probability percentage.
• Keep a copy. Save your report somewhere secure, whether digital or printed. You may need it for legal proceedings, insurance matters, or personal records down the road.

If anything on the report looks off or does not make sense, contact the lab directly. Good testing providers have support staff who can walk you through the report and answer your questions. For more on testing accuracy and reliability, the article on home paternity test accuracy breaks down the science behind the numbers. You can also read about common misconceptions about DNA testing if something still feels unclear.

Frequently Asked Questions

What Percentage Confirms Paternity?

A probability of paternity of 99% or higher is considered definitive proof of biological fatherhood. Most confirmed results come in at 99.99% or above. Courts, government agencies, and accredited labs worldwide treat these figures as conclusive. The number never reaches exactly 100% because of how the statistics work, not because there is any doubt.

What Is a Combined Paternity Index?

The Combined Paternity Index, or CPI, tells you how many times more likely it is that the tested man is the biological father compared to a random, unrelated man. The lab calculates a paternity index for each genetic marker tested and multiplies them all together to get the CPI. A CPI of 100,000 means the tested man is 100,000 times more likely to be the father. The CPI is what the lab uses to calculate the probability of paternity percentage.

Can I Get a Printed Copy of My Results?

Yes. Most providers deliver results through a secure online portal, but printed copies are available too. For legal paternity tests, a printed report with original signatures is standard and gets mailed to you for court submission. For at-home peace of mind tests, you can usually download and print from the portal, or ask the lab to mail you a copy.

What If the Tested Man and the Real Father Are Related?

If the alleged father and the actual biological father are close relatives, like brothers or father and son, they share more DNA than unrelated people. That can sometimes push the probability higher than it should be if the wrong relative was tested. Testing more genetic markers reduces this risk by picking up subtle differences in their profiles. US Diagnostics Center tests up to 28 markers, which helps tell related men apart. If you know two potential fathers are related, let the lab know so they can use the right statistical analysis. The article on home vs. legal paternity testing has more on how DNA is shared among relatives.

How Do I Read the Allele Numbers on My Report?

The allele numbers in the genetic marker table are specific genetic variants found at each tested location on the DNA. Each person has two allele numbers per locus, one from each parent. To check for paternity, look at each row and see if at least one of the child's numbers matches one of the alleged father's numbers at the same locus. Matching across all or nearly all markers supports a confirmation. You do not need to understand what the numbers themselves mean. They are just identifiers the lab uses to compare profiles.

This article is part of our Paternity Testing: The Complete Guide guide.