A parent with type A may carry AA or AO, so the chances depend on how common the hidden O allele is. Two type O parents can only have type O children, while two Rh-positive parents can have an Rh-negative child if both carry the d allele. Everything is calculated in your browser, so nothing you type is sent to our server.
How to use the Blood Type Calculator
- Mother – ABO group
- Mother – Rh
- Father – ABO group
- Father – Rh
Everything runs in your browser, so results appear instantly and nothing you type is sent to a server.
How it works
Choose each parent’s ABO group and Rh type.
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
ABO: alleles A and B are co-dominant with each other and dominant over O
Rh: D (positive) is dominant over d (negative)
Each parent passes one allele at random; parental genotypes are weighted by population frequencies
Worked example
Inputs — Mother – ABO group: A; Mother – Rh: Rh positive; Father – ABO group: B; Father – Rh: Rh negative.
Results — Most likely blood type = AB+ (21.3%); Type A = 26.9%; Type B = 22.8%; Type AB = 29.5%; Type O = 20.8%; Rh positive = 72.1%.
Key terms
- Allele
- One version of a gene.
- Genotype
- The pair of alleles a person carries.
Frequently asked questions
Can two O parents have an A child?
Not under normal inheritance – rare exceptions exist (such as the cis-AB or Bombay phenotypes).
Can two Rh-positive parents have an Rh-negative child?
Yes, if both carry the recessive d allele.
Can blood type prove paternity?
It can sometimes exclude a father, but only DNA testing proves paternity.