Baby Blood Type Calculator

What the result tells you

This baby blood type calculator shows a set of blood types that may fit the ABO and Rh selections for two parents. Choose each parent's reported A, B, AB, or O group and Rh+ or Rh− status. The result combines possible ABO groups with possible Rh signs, and separately lists ABO groups excluded by the simplified model. It is a teaching aid for exploring inheritance patterns, not a test result or a probability estimate.

ABO groups come from inherited alleles

In the common ABO model, a child receives one allele from each parent. A and B are expressed together when both are inherited; O is recessive in relation to A and B. This means a person with type A may have genotype AA or AO, and a person with type B may have BB or BO. The calculator accepts the visible blood group, not a parent's underlying genotype, so it includes outcomes compatible with those possible genotypes.

ABO combinations at a glance

Swapping which parent is listed first does not change the possible ABO set. In the result area, a label such as A+ combines the ABO group with the Rh sign.

How the Rh sign is handled

The page uses a simplified RhD-style positive/negative model. If both parents are entered as Rh−, the listed combinations carry a negative sign. If either parent is entered as Rh+, both signs are included in the possible set. This is a broad possibility rule; a positive phenotype alone does not reveal the exact inherited variant or genotype. The Rh system includes more antigens and variants than this two-sign model represents.

Enter reported types and read each result area

1. Use a known blood type

   Refer to a reliable blood typing record for each parent. This page cannot determine either parent's type from family history.

2. Select both ABO groups

   Choose A, B, AB, or O separately for the father and mother. The results recalculate when a selection changes.

3. Add the Rh signs

   Select Rh+ or Rh− for each parent. Possible results combine the ABO groups with the supported signs, for example A+ or O−.

4. Distinguish possible from excluded

   The possible area shows full ABO-and-Rh combinations. The excluded area lists ABO groups only; it does not show excluded plus/minus combinations.

For example, selecting A+ and O− gives possible ABO groups A and O, with both Rh signs shown for those groups. B and AB appear in the excluded ABO list. This example describes the calculator's simplified output, not the chance of each outcome.

Questions about possible outcomes

Limits of a simplified inheritance model

Use these results for general education about common ABO and simplified RhD possibilities only.

• Not a blood test: Confirm a person's blood type through appropriate laboratory testing. Do not use a family combination as an individual's medical record.
• Not a clinical decision tool: The results are not for transfusion matching, prenatal diagnosis, pregnancy risk assessment, or treatment decisions. RhD-negative pregnant people should follow local prenatal screening advice; the NHS describes screening and care for HDFN, but local practice may differ.
• Exceptions exist: ABO subgroups and rare phenotypes, plus weak or partial D and other Rh antigens, are not represented by the selections. A real laboratory result or a clinician's interpretation takes precedence if it differs from this teaching model.
• No probabilities or genotype inference: The displayed sets do not indicate which outcome is more likely and cannot reveal the parents' specific genetic makeup.