Paternity DNA Testing: Types, Accuracy & Process
Content last reviewed 2026-09-12 · Educational information — not medical advice
Quick answer
Modern paternity testing compares 20+ DNA markers achieving 99.99%+ inclusion probability or 100% exclusion. Legal-chain-of-custody versions (witnessed collection, documentation) satisfy courts; informational home kits trade admissibility for convenience.
Accuracy mechanics
Each DNA locus follows Mendelian rules — child inherits one allele per parent. Testing 20 STR markers mathematically excludes non-fathers absolutely (two mismatched loci suffice) and includes true fathers at combined-paternity-index values translating to 99.99%+. Adding the mother's sample strengthens statistics though father-child duos work fine.
Legal versus informational testing
| Feature | Legal test | Informational/home kit |
|---|---|---|
| Chain of custody | witnessed, ID-verified collection | self-collected, mail-in |
| Court admissibility | yes (child support, custody, immigration) | no |
| Convenience | appointment required | arrives at door |
| Cost | $300-600 | $80-200 |
Practical considerations before testing
Prenatal non-invasive options (cell-free fetal DNA from maternal blood, from ~8 weeks) exist at premium costs versus post-birth cheek swabs. Emotional sequencing matters: results permanently alter family narratives — counseling resources help many navigate pre/post-result dynamics. Immigration cases require AABB-accredited facilities specifically.
Beyond paternity
Same technology covers maternity, siblinghood (full/half), grandparent reconstruction (when alleged father unavailable), and twin zygosity — each relationship type carrying distinct statistical frameworks and collection protocols.
Frequently asked questions
Can home-kit results become legal later?
No — chain-of-custody breaks forever at self-collection; courts require witnessed processes from the start.
Do medications affect results?
Nothing chemical alters DNA — transfusions/bone-marrow transplants create rare exceptions worth disclosing.