Blood Type Calculator — ABO and Rh Inheritance

Use the Blood Type Calculator

Enter each parent’s ABO and Rh type to see all possible child outcomes. The blood type calculator shows separate ABO and Rh distributions and a combined list with percentages.

Enter parent blood types

How to Use Blood Type Calculator — ABO and Rh Inheritance

1. Step 1: Select parent blood types

   Choose ABO and Rh for Parent 1 and Parent 2 (e.g., A+, O−). Results update instantly.

2. Step 2: Open advanced options (optional)

   If you know genotypes, set AA vs AO, BB vs BO, and DD vs Dd to refine the percentages.

3. Step 3: Review distributions

   Check the ABO distribution, the Rh distribution, and the combined ABO+Rh outcomes.

4. Step 4: Compare scenarios

   Try different pairings or zygosity settings to see how possibilities change for a child.

5. Step 5: Save or share

   Screenshot your results for personal notes. For medical decisions, rely on lab testing.

Key Features

• ABO outcomes with percentages
• Rh factor distribution
• Combined ABO+Rh possibilities
• Advanced genotype options (AA/AO, BB/BO, DD/Dd)

Understanding Results

Formula

ABO types result from combinations of the A, B, and O alleles: AA or AO yields type A; BB or BO yields type B; AB yields AB; OO yields O. Rh uses the D antigen: any genotype with at least one D (DD or Dd) is Rh+, while dd is Rh−. The calculator combines parent genotypes (or default assumptions) to compute the probability of each child outcome.

Interpreting ABO + Rh outcomes

Review ABO and Rh distributions separately, then use the combined list to see the overall likelihood for each child blood type. Advanced genotype settings refine these percentages.

Inheritance caveats and edge cases

Real populations include rare variants (for example, Bombay phenotype for ABO or weak D for Rh) that basic charts don’t capture. Use lab testing for clinical decisions; treat this blood type calculator as an educational overview.

Blood type calculator examples

Two O parents can only have O children. A parent with AB and a parent with O yield either A or B — never AB or O. Two Rh− parents always produce Rh− children, while two Rh+ parents can produce Rh+ and sometimes Rh− depending on their genotypes (DD vs Dd). Use advanced options if you know AA vs AO, BB vs BO, or DD vs Dd.

Using advanced genotype options

If you know whether a parent with type A is AA or AO (or B is BB or BO), set that in Advanced. Likewise choose DD or Dd for Rh+. The blood type calculator will refine the child outcome percentages instantly.

Reference Ranges & Interpretation

There is no “normal” or “abnormal” blood type—only distributions of possibilities based on the parents. For example, AB × O can produce A or B only; O × O yields O only; A × B can yield all four ABO types if both carry O. Rh follows its own rules: two Rh− parents produce Rh− children, while Rh+ parents can produce Rh+ and, in some pairings, Rh−.

Assumptions & Limitations

By default, when phenotype could come from two genotypes (A → AA/AO, B → BB/BO, Rh+ → DD/Dd), we treat those options as equally likely. You can override this under advanced options. Real populations vary, and rare phenotypes (e.g., Bombay, weak D) can differ from basic charts. For medical decisions, rely on lab testing and professional care.

Complete Guide: Blood Type Calculator — ABO and Rh Inheritance

Use the blood type calculator to explore a child’s possible ABO and Rh types from two parents. View outcomes and percentages, plus advanced genotype settings. Our blood type calculator models ABO and Rh inheritance to show every child blood type that is possible, plus estimated percentages under clear, adjustable assumptions. It stays mobile‑friendly and fast: choose parent blood types, open advanced options if you know genotypes, and see outcomes update instantly.

ABO and Rh in plain English

A person’s “blood type” has two parts: an ABO type (O, A, B, or AB) and the Rh factor (negative “−” or positive “+”). ABO refers to the presence or absence of A and B antigens on the surface of red blood cells. If you have A antigens, you’re type A; B antigens, type B; both A and B, type AB; neither, type O. Separately, Rh describes the D antigen: if it’s present you are Rh positive; if not, Rh negative.

ABO inheritance uses codominance for A and B, while O is recessive. That means A or B “shows” even when paired with O, but O only appears when a child receives O from both parents. Rh inheritance is simpler: positive (D) is dominant over negative (d). A single D typically yields Rh+. These two systems are inherited independently, so the calculator shows ABO and Rh results separately and combined.

Quick recap: ABO + Rh patterns

Two O parents yield O only; an A parent and an O parent can yield A or O; AB with O yields A or B; and Rh+ can mask Rh− unless both parents are Rh−. Use the blood type calculator to test these patterns with adjustable assumptions.

Why a blood type calculator helps

The blood type calculator turns the ABO and Rh rules into clear percentages you can explore with a few taps. It’s useful for classroom learning, family curiosity, and planning questions to ask a clinician—never for clinical decisions.

Genotype vs phenotype (AA/AO, BB/BO, DD/Dd)

A visible blood type (phenotype) can arise from more than one genotype. For example, type A may be AA or AO, and Rh+ may be DD or Dd. Our calculator lets you adjust these assumptions to refine child outcome percentages. If you don’t know genotypes, the tool starts with reasonable 50/50 priors and clearly shows how toggling them changes the results.

Why does this matter? Beyond being a fascinating biology topic, blood group systems are foundational to safe transfusions and certain aspects of prenatal care. Understanding the broad patterns helps you interpret what you see in the calculator and in common inheritance diagrams, while recognizing that laboratories always confirm blood type directly before any clinical decision.

How inheritance works

Each parent passes one ABO allele and one Rh allele to the child. A parent with type A can be genetically AA (homozygous) or AO (heterozygous). A parent with type B can be BB or BO. AB is always AB, and O is always OO. For Rh, a positive parent can be DD or Dd; a negative parent is dd. If you don’t know whether an A parent is AA or AO (or a B parent is BB or BO, or an Rh+ parent is DD or Dd), leave the advanced options closed. The calculator uses a balanced mix of those possibilities by default so you still get clear, realistic outcomes.

When you open advanced genotype options, you can choose AA vs AO (for type A), BB vs BO (for type B), and DD vs Dd (for Rh+). The app updates results instantly. These settings matter because genotype changes the gametes a parent can pass. For example, an AO parent passes A or O with equal probability, while an AA parent only passes A. When the other parent’s possibilities combine with those gametes, the child’s phenotype distribution (A, B, AB, O and Rh+/Rh−) emerges.

If you like Punnett squares, you can imagine each parent contributing one allele across a 2×2 or 4×4 grid depending on the scenario. The calculator essentially does that combinatorics under the hood—weighting each square by the likelihood that a parent has a particular genotype and the probability of passing each allele. The final percentages you see are the totals after combining all squares.

Rh factor explained

Rh can matter during pregnancy when an Rh− mother conceives an Rh+ fetus. Health professionals may offer Rh immune globulin at specific times during and after pregnancy to help reduce the chance of sensitization. While our tool explains inheritance possibilities, it does not diagnose, treat, or replace clinical care. If you have concerns about Rh compatibility, speak with your clinician for guidance tailored to your situation.

Most people are Rh+. In practical terms, if both parents are Rh−, every child will be Rh−. If one parent is Rh+ and carries at least one D, Rh+ becomes possible. If both parents are Rh+, there’s a chance for Rh− only if both carry a recessive d (Dd × Dd can produce dd). Our calculator captures these scenarios automatically.

Worked examples (A×O, AB×O, O×O, AB×AB)

A × O (unknown genotype): If the A parent is AA, every child is type A. If the A parent is AO, each child has a 50% chance for A and a 50% chance for O. When genotype is unknown, our default uses a 50–50 mix of AA and AO, so the results show both A and O outcomes overall. Types B and AB are not possible in this pairing.

AB × O: Possible ABO outcomes are A or B only (never AB or O), because the AB parent contributes A or B while the O parent contributes O. The combinations AO and BO map to phenotypes A and B respectively. Exact percentages depend on the AB parent contributing A or B and the Rh genotypes involved.

A × B (both unknown): This classic case can yield any ABO phenotype depending on whether each parent carries O. If both are heterozygous (AO and BO), the child’s ABO distribution is 25% O, 25% A, 25% B, and 25% AB before considering Rh. If one parent is homozygous (AA or BB), O becomes less likely or impossible, respectively. The advanced options help you specify what you know.

Worked examples continued (quick mid‑summary)

So far, the key idea is that O requires OO, while A and B dominate when paired with O. Keep that in mind as you scan the next pairings—notice how the presence or absence of O explains which results can and cannot appear.

O × O: Both parents can only pass O, so children are always type O. The Rh outcome depends on the parents’ Rh genotypes. Two Rh− parents (dd × dd) will have Rh− children. If one parent is Rh+ and carries D, then Rh+ becomes possible in the distribution.

AB × AB: Children can be AB, A, or B (never O), because O requires OO and neither AB parent carries O. Rh results depend on whether either parent is DD or Dd.

Rh examples — A− × B+: Suppose the A parent is Rh− (dd) and the B parent is Rh+ with unknown genotype (DD or Dd). If the B parent is DD, every child will be Rh+. If the B parent is Dd, each child has a 50% chance of Rh+ and a 50% chance of Rh−. Our default “unknown mix” splits those genotypes evenly to show both outcomes.

Key takeaways from the worked examples

O behaves recessively, so it only appears when both parents can pass O; AB with O yields only A or B; and A×B can yield any ABO type when both carry O. Rh+ can mask Rh− unless both parents are Rh− or carry a recessive d. Keep these patterns in mind as you adjust genotypes in the calculator.

Interpreting blood type calculator results

Use the blood type calculator as an educational guide to what is possible. If a displayed outcome looks surprising, adjust the advanced genotype options and try variants like AO vs AA or DD vs Dd. For any decision that depends on blood type, a laboratory test remains the standard.

Using advanced options: Imagine a family where one parent knows they’re AO (confirmed by testing or by having an O child with an O partner), while the other parent is BO. Selecting AO and BO fixes the ABO distribution at 25% O, 25% A, 25% B, and 25% AB before Rh is considered. This level of control helps you explore scenarios based on what you actually know, instead of guessing or relying on broad population assumptions.

Probabilities and assumptions

A simple way to present probabilities—without guessing population‑specific genetics—is to assume that when more than one genotype can produce a phenotype, those genotypes are equally likely. That’s what our calculator does by default: A is treated as AA or AO with equal weight; B as BB or BO; Rh+ as DD or Dd. This keeps results intuitive for most users. If you know a parent’s genotype from testing or family patterns (for example, two O parents produced an A child—suggesting a non‑O allele elsewhere), set the advanced options accordingly and the percentages will adjust.

Real populations can deviate from these priors. Rh− is relatively uncommon worldwide, and the proportion of AO vs AA (or BO vs BB) varies by ancestry. That’s why it’s best to treat the default outputs as educational estimates rather than clinical probabilities. Laboratory testing remains the standard for decisions.

Another subtlety is rounding. The calculator rounds to whole percentages for readability and ensures totals sum to 100%. That means small categories might show 1% or 0% depending on the scenario and rounding rules. The underlying math still tracks precise fractions before rounding.

Keep in mind that ABO and Rh are only two of dozens of recognized blood group systems. For inheritance education, they’re the most widely taught and the easiest to visualize. For transfusion safety, professionals consider additional systems and perform crossmatching to confirm compatibility in the lab.

Compatibility, transfusion basics, and practical uses

Family‑planning and classroom learning are the two most common uses for inheritance calculators. They are a fun way to visualize genetics and to start conversations with a healthcare professional when you have questions about Rh or about a child’s possible blood type.

Transfusion compatibility is a separate, tightly controlled topic. Hospitals and blood banks rely on exact laboratory testing and crossmatching performed by trained staff. Never use an online tool to make decisions about transfusion safety, donor/recipient matching, or clinical management in pregnancy. If you ever need a transfusion, the medical team will confirm your blood type directly.

Parents and students also use blood type charts to understand why certain outcomes never appear. For example, two type O parents cannot have a child with type A, B, or AB, because neither parent carries A or B to pass on. On the other hand, A and B parents can, in principle, have any ABO type, depending on whether each carries an O. The calculator helps test these rules instantly without drawing a Punnett square by hand.

Expecting or planning? You might also find these tools helpful: Ovulation Calculator, Period Calculator, Pregnancy Due Date Calculator (EDD), Baby Growth Calculator, and Vaccination Schedule Calculator.

Limitations and rare cases

Genetics can be more complex than ABO and Rh basics suggest. Rare phenotypes exist. The Bombay (Oh) phenotype can appear O on routine testing but has unique transfusion needs. Some individuals have “weak D” variants that can test Rh− on some assays and Rh+ on others. Transplants, chimerism, and particular conditions can also affect what a basic blood type test shows at a given time. Our calculator is designed for typical inheritance patterns and for education—not for clinical decisions.

If your family has unusual lab results or you’ve been told you have a rare blood group, ask your clinician for a thorough explanation and documentation. Authoritative overviews are available from reputable medical sources such as MedlinePlus Genetics and the Centers for Disease Control and Prevention (CDC). MedlinePlus — Blood typing and CDC — Blood Safety (About) provide helpful background.

Subgroups such as A1 and A2 can influence technical laboratory interpretation without changing the basic inheritance concepts taught in high‑school biology. Likewise, rare cis‑AB alleles and other uncommon genetic arrangements can produce patterns that differ from standard charts. These exceptions are meaningful in the lab, but they are not necessary for understanding everyday inheritance with our calculator.

Next steps and related tools

Use the calculator above to try different parent combinations. Keep the defaults if genotypes are unknown, or open advanced options to set AA/AO, BB/BO, and DD/Dd specifically. The cards will show the ABO distribution, the Rh distribution, and the combined possibilities for the child. Scroll further down the page to read the FAQs and view related tools.

Results are educational, not diagnostic. If a medical decision depends on blood type, a laboratory test is required. For pregnancy planning, also consider tools that help with timing and milestones, including the Ovulation Calculator and the EDD Calculator.

If you’re curious about growth after birth, the Baby Growth Calculator provides size curves over time, and the Vaccination Schedule Calculator helps plan recommended doses. These tools are designed to complement each other while keeping your data private.

Frequently Asked Questions