🩸Blood Type Compatibility Calculator
Check red-cell transfusion compatibility for any blood type, or predict the blood types a child could inherit from their parents — instantly, no sign-up.
Full Red-Cell Compatibility Chart
← scroll to see the full table →
| Recipient ↓ / Donor → | O− | O+ | A− | A+ | B− | B+ | AB− | AB+ |
|---|
✓ = compatible for red-cell transfusion. Plasma and platelet compatibility rules differ; this tool covers red cells only.
This tool is for educational purposes only and is not medical advice. Real transfusions and any medical decisions require testing and assessment by qualified healthcare professionals.
Free Blood Type Compatibility Calculator Online
Curious who can donate blood to whom — or what blood type your child might have? Our free Blood Type Calculator answers both the moment you make a selection. As a clear and accurate blood type compatibility tool, it shows transfusion compatibility for any blood type, telling you exactly which types a donor can give to and which a recipient can receive from, across all ABO groups and Rh factors.
But it does more than compatibility. Enter two parents' blood types and it predicts the possible blood types their child could have, based on standard ABO and Rh inheritance. Whether you're a student learning genetics, brushing up on transfusion rules, or simply curious, the answers are laid out simply and clearly. Simply choose your blood types to see the results instantly. No sign-up, no downloads, no limits — just clear, educational answers whenever you need them.
Blood Type Compatibility for Transfusions
In red-cell transfusions, compatibility depends on the ABO blood group and the Rh (Rhesus) factor. O− is the universal donor — its red cells carry no A, B, or Rh antigens and can be given to patients of any blood type. AB+ is the universal recipient — it can receive red cells from all eight blood types. Between these extremes, the rules follow a clear pattern: Rh− donors can donate to both Rh− and Rh+ recipients, while Rh+ donors can only donate to Rh+ recipients. For ABO, type O donates to any group, while types A, B, and AB donate within their respective groups and upward to AB.
Predicting a Child's Blood Type
Blood type is inherited through ABO alleles — A and B are codominant, O is recessive — and the Rh factor, where Rh+ is dominant and Rh− is recessive. Each parent passes one allele of each to their child. Because a type-A parent may be AA or AO, and a type-B parent may be BB or BO, the set of possible child types is wider than the parents' types alone suggest. The calculator shows all outcomes consistent with standard ABO and Rh genetics for the selected parent combination.
Educational Use Only
This tool is educational and intended as a learning aid or quick reference. Real blood transfusions require laboratory cross-matching and compatibility testing performed by qualified medical professionals. Child blood type results reflect genetic possibilities, not guaranteed outcomes. For any clinical or medical decision, always consult a qualified healthcare provider.
About the Blood Type Compatibility Calculator
Key features
Transfusion compatibility
Select any blood type to see who it can donate to and receive from, for red-cell transfusion. Covers all eight ABO/Rh types with a full compatibility chart for reference.
Universal donor & recipient
O− is the universal red-cell donor; AB+ is the universal recipient. The calculator highlights these automatically when either type is selected.
Child blood type prediction
Enter two parents' blood types to see all possible child blood types, based on ABO allele inheritance (including AA/AO and BB/BO genotype ambiguity) and Rh factor rules.
Reference matrix
A full 8×8 compatibility chart shows all donor/recipient combinations at a glance. It highlights the selected type's row and column for quick cross-referencing, and scrolls horizontally on small screens.
ABO and Rh basics
ABO blood groups
Determined by the antigens on red blood cells. Type O has no A or B antigens. Type A has A antigens. Type B has B antigens. Type AB has both. These antigens determine which types the immune system will attack.
Rh factor
The Rh (Rhesus) antigen is either present (Rh+) or absent (Rh−). Rh+ is dominant — one copy of the allele is enough. Rh− requires two recessive copies. Rh+ donors can only give to Rh+ recipients; Rh− can give to either.
ABO inheritance
A and B alleles are codominant; O is recessive. Each parent passes one allele. A type-A parent may be AA or AO; a type-B parent may be BB or BO. This is why two type-A parents can sometimes have an O-type child.
Educational use only
Have questions? See the Blood Type Calculator FAQ.
Frequently Asked Questions
How does the blood type calculator work?
Select a blood type to see its transfusion compatibility — who it can donate to and receive from — or enter two parents' blood types to see the blood types their child could have, based on standard ABO and Rh inheritance.
Is this calculator free to use?
Yes, it's completely free with no sign-up, downloads, or limits. Use it as often as you like.
Which blood type is the universal donor?
O negative (O−) is known as the universal red-cell donor because it carries no A, B, or Rh antigens and can be given to people of any ABO and Rh type. AB positive (AB+) is the universal recipient, able to receive red cells from any type.
What do ABO and Rh mean?
ABO refers to the A, B, AB, and O blood groups, determined by which antigens are present on your red blood cells. Rh (Rhesus) is the positive/negative factor — Rh+ means the Rh antigen is present, Rh− means it is absent. Together they make up the common eight blood types: A+, A−, B+, B−, AB+, AB−, O+, and O−.
How does it predict a child's blood type?
Each parent passes one ABO allele (A, B, or O) and one Rh allele to their child. The tool combines the parents' possible alleles — accounting for the fact that type A can be genotype AA or AO, and type B can be BB or BO — to show which blood types a child could inherit, and which are not possible.
Is the child blood type result a certainty?
No — it shows the possible outcomes and, where relevant, which types cannot occur. Actual inheritance depends on each parent's specific genotype, which a blood type alone does not fully reveal. A type-A parent could be AA or AO; only genetic testing can confirm which.
Does compatibility differ for plasma versus red cells?
Yes. The rules for plasma donation are effectively the reverse of red-cell donation — AB is the universal plasma donor and O is the universal plasma recipient. This tool focuses on red-cell transfusion compatibility, which is the most commonly referenced context.
Is my data stored anywhere?
No. Your selections are processed directly in your browser and are never stored or sent to a server, keeping your information completely private.
Does it work on mobile devices?
Yes, the calculator is fully responsive and works on smartphones, tablets, and desktops. The compatibility chart scrolls horizontally on smaller screens rather than forcing the page wider, so all content remains accessible without overflow.
Can I rely on this for a real transfusion or medical decision?
No. This tool is educational. Real transfusions involve cross-matching and additional testing by medical professionals. Always rely on qualified healthcare providers for any actual medical decision.