# Blood Type Calculator

Predict your child's possible blood types based on both parents' ABO and Rh blood types. Uses Mendelian genetics with probability breakdown.

## What this calculates

Blood type is inherited through Mendelian genetics. This calculator predicts possible blood types for a child based on both parents' ABO blood types and Rh factors, with probability percentages for each possible outcome.

## Inputs

- **Parent 1 Blood Type** — options: A, B, AB, O
- **Parent 1 Rh Factor**
- **Parent 2 Blood Type** — options: A, B, AB, O
- **Parent 2 Rh Factor**

## Outputs

- **Possible Blood Types** — formatted as text — ABO blood types the child could have
- **Possible Rh Factors** — formatted as text — Rh factor possibilities for the child
- **Probability Breakdown** — formatted as text — Detailed probability for each blood type combination

## Details

Blood type is determined by two gene systems: ABO and Rh. The ABO system has three alleles — A, B, and O — where A and B are codominant and both are dominant over O. Each person inherits one ABO allele from each parent. Type A blood can have genotype AA or AO, type B can be BB or BO, type AB is always AB, and type O is always OO. The Rh factor is determined by the presence (Rh+) or absence (Rh–) of the D antigen, controlled by the RHD gene. Rh positive (D allele) is dominant over Rh negative (d allele).

Since phenotype (what we see) does not always reveal genotype (genetic makeup), the calculator uses probability-weighted estimates. For example, a parent with type A blood could be AA (homozygous) or AO (heterozygous), and since AO is more common in most populations, this affects the probability of each child blood type. The probabilities shown assume that heterozygous genotypes are twice as likely as homozygous for A and B types.

This calculator provides educational estimates. Actual blood type must be determined through laboratory testing. The predictions are based on simple Mendelian inheritance and do not account for rare variants, mutations, or Bombay phenotype.

## Frequently Asked Questions

**Q: Can two type O parents have a non-O child?**

A: No. Two type O parents both have the genotype OO, meaning they can only pass O alleles to their children. All children will be type O. This is the most predictable blood type combination.

**Q: Can two Rh-positive parents have an Rh-negative child?**

A: Yes. If both parents are heterozygous (Dd), there is a 25% chance their child will be Rh-negative (dd). Since many Rh-positive people are heterozygous carriers, this is relatively common.

**Q: Why do the probabilities not always add to familiar ratios?**

A: Because we do not know each parent's exact genotype from their blood type alone. A parent with type A could be AA or AO. The calculator uses probability-weighted estimates that account for both possibilities, which produces blended percentages rather than clean Punnett square ratios.

**Q: What is the rarest blood type?**

A: AB negative is the rarest blood type, found in less than 1% of the global population. The most common type varies by ethnicity: O positive is most common worldwide (~38%), while in some Asian populations, B positive is more prevalent.

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Source: https://vastcalc.com/calculators/health/blood-type
Category: Health & Fitness
Last updated: 2026-04-21