# Blood Type Calculator (Child’s Blood Type from Parents)

URL: https://speedycalculator.com/calculators/health/blood-type/
Last updated: 2026-10-30

> The blood type calculator predicts the possible ABO and Rh blood types of a child from the parents' blood types, with the probability of each, using Mendelian inheritance and typical population gene frequencies.

## Inputs

- Mother – ABO group
- Mother – Rh
- Father – ABO group
- Father – Rh

## Results

- Most likely blood type
- Type A
- Type B
- Type AB
- Type O
- Rh positive
- Rh negative
- All combinations

## Formula

```
ABO: alleles A and B are co-dominant with each other and dominant over O
Rh: D (positive) is dominant over d (negative)
Each parent passes one allele at random; parental genotypes are weighted by population frequencies
```

## Explanation

A parent with type A may carry AA or AO, so the chances depend on how common the hidden O allele is. Two type O parents can only have type O children, while two Rh-positive parents can have an Rh-negative child if both carry the d allele. Everything is calculated in your browser, so nothing you type is sent to our server.

### How to use the Blood Type Calculator

- **Mother – ABO group**
- **Mother – Rh**
- **Father – ABO group**
- **Father – Rh**

Everything runs in your browser, so results appear instantly and nothing you type is sent to a server.

### How it works

Choose each parent's ABO group and Rh type.

*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — Mother – ABO group: A; Mother – Rh: Rh positive; Father – ABO group: B; Father – Rh: Rh negative.

Results — **Most likely blood type = AB+ (21.3%)**; Type A = 26.9%; Type B = 22.8%; Type AB = 29.5%; Type O = 20.8%; Rh positive = 72.1%.

## Key terms

- **Allele**: One version of a gene.
- **Genotype**: The pair of alleles a person carries.

## FAQ

**Can two O parents have an A child?**
Not under normal inheritance – rare exceptions exist (such as the cis-AB or Bombay phenotypes).

**Can two Rh-positive parents have an Rh-negative child?**
Yes, if both carry the recessive d allele.

**Can blood type prove paternity?**
It can sometimes exclude a father, but only DNA testing proves paternity.


## Sources

- [Dean L. Blood groups and red cell antigens. NCBI, 2005](https://www.ncbi.nlm.nih.gov/books/NBK2261/)