Blood Type Calculator
Check donation compatibility, or work out which blood types a child could inherit from two parents.
- You can receive from
- —
- Share of population
- —
- Cannot be
- —
How blood compatibility works
Your immune system attacks any blood antigen it has not met, so a donor's antigens must be a subset of the recipient's. Type O red cells carry neither A nor B antigen, which is why O negative can be given to anyone and is what ambulances carry. Type AB carries both, so AB positive patients can receive from anyone. Plasma works the opposite way round — AB is the universal plasma donor and O the universal plasma recipient — because plasma carries the antibodies rather than the antigens.
Red cell compatibility
| Type | Can donate to | Can receive from | US population |
|---|---|---|---|
| O− | Everyone | O− | 7% |
| O+ | O+, A+, B+, AB+ | O−, O+ | 38% |
| A− | A−, A+, AB−, AB+ | O−, A− | 6% |
| A+ | A+, AB+ | O−, O+, A−, A+ | 34% |
| B− | B−, B+, AB−, AB+ | O−, B− | 2% |
| B+ | B+, AB+ | O−, O+, B−, B+ | 9% |
| AB− | AB−, AB+ | O−, A−, B−, AB− | 1% |
| AB+ | AB+ | Everyone | 3% |
Population figures are approximate US frequencies and vary considerably by ancestry — Rh negative is much rarer in East Asian populations, for instance.
How a child inherits blood type
ABO type comes from two alleles, one from each parent. A and B are codominant; O is recessive. So a parent who is type A carries either AA or AO, and can pass on an O allele without being type O themselves.
Rh works the same way: an Rh positive parent may carry a hidden negative allele, so two Rh positive parents can have an Rh negative child. Two Rh negative parents, however, have no positive allele to pass on, so their child must be Rh negative.
One well-known exception: the extremely rare Bombay phenotype produces results that appear to break the rules, which is why blood typing alone is not accepted as proof of parentage.
How to use the Blood Type Calculator
- Choose whether you are checking donation compatibility or a child’s possible types.
- Select the blood type or the two parents’ types.
- Read who can give and receive, or which types a child could and could not be.
Frequently asked questions
What is the universal blood donor?
O negative, for red cells. It carries no A, B or Rh D antigen, so it can be transfused into any patient — which is why it is stocked for emergencies before a patient can be typed.
What is the universal recipient?
AB positive. Those patients already have A, B and Rh D antigens, so their immune system does not attack any donor red cells.
Can two O parents have an A child?
No. Type O carries only O alleles, so both parents can only pass on O. Any apparent exception points to an extremely rare genetic variant or a mistake in the typing.
Can blood type prove parentage?
It can exclude a possibility but never confirm one, and rare phenotypes make even exclusions unreliable. DNA testing is the only sound method.
Why is plasma compatibility the other way round?
Because plasma carries antibodies rather than antigens. Type AB plasma has neither anti-A nor anti-B antibodies, making AB the universal plasma donor — the reverse of red cells.
Related tools
Last reviewed September 4, 2026. Educational only. Blood typing for medical or legal purposes requires a laboratory test.