Understanding your paternity test results
A DNA paternity test returns one of two answers: inclusion ("probability of paternity 99.99%+", meaning the alleged father is the biological father) or exclusion ("probability of paternity 0%", meaning he is definitively not). No properly conducted AABB-accredited test returns "maybe" or "50%". The 99.99% figure is a statistical certainty threshold — never 100%, because 100% would require ruling out every human on earth.
What "99.99% probability of paternity" means
Probability of paternity is a statistical measure of how likely it is that the tested man is the biological father, compared to a random man from the same population. When you see 99.99% (or often 99.9999%+), it means the genetic evidence is overwhelmingly consistent with paternity — a random unrelated man would have less than a 1-in-10,000 chance of matching the child at every tested marker. Above 99% is the industry-accepted threshold for inclusion.
Why never 100%?
A result of exactly 100% would only be provable by testing every human being on earth and ruling each one out. Statistically, that's impossible — so paternity science uses 99.99%+ as its definitive inclusion threshold. This is the same standard used in courts, immigration, and forensic labs worldwide.
What "0% probability" means (exclusion)
Exclusion is mathematically definitive. If even a few of the 34 tested markers show the child could not have inherited the alleged father's DNA, he is ruled out completely. There is no "close" exclusion — one mismatched marker isn't enough to exclude (mutation is possible), but multiple mismatches produce a definitive 0%.
Combined Paternity Index (CPI)
The CPI is a ratio: how much more likely the alleged father is to have contributed the child's DNA than a random man. A CPI of 10,000 means 10,000 times more likely. The final probability of paternity is calculated from the CPI using a formula (Bayesian, assuming 50% prior probability). CPI numbers are often in the millions or billions in modern 34-marker tests.
34 markers, explained
Modern paternity tests read 34 short tandem repeat (STR) markers — regions of DNA that vary widely between individuals. Each marker has two values, one from each biological parent. If the alleged father is the biological father, every one of the child's paternal marker values will match one of his. If he isn't, mismatches at multiple markers will rule him out.
What your PDF will show
- Each of the 34 markers listed by name with the values for father, child, and (if included) mother
- The Paternity Index for each marker
- The Combined Paternity Index (CPI) across all markers
- The final Probability of Paternity — 99.99%+ or 0%
- Signature of the AABB-accredited lab director
Ready for a clear answer?
AABB-accredited lab. All fees included. Results in 1–2 business days.