Blood Type Inheritance Predictor
Pick each parent's blood type and Rh factor to see the chance of each baby blood type, assuming A, B and Rh+ parents carry a hidden O or Rh- gene. How it works
Use the Blood Type Inheritance Predictor
About the Blood Type Inheritance Predictor
If both carry a hidden O gene, parents with blood types A+ and B+ can have a child of type A, B, AB or O at 25% each, and Rh+ at 75% or Rh- at 25%, so an A+ child is 18.75%. The predictor assumes every type A or B parent carries O and every Rh+ parent carries Rh-, because a blood type alone cannot show it. A parent with a type O parent of their own does carry O; a parent who is really AA or BB cannot have an O child.
Child blood type chances for common parent pairs
| Parents | A | B | AB | O | Rh+ | Rh- |
|---|---|---|---|---|---|---|
| A+ × B+ | 25% | 25% | 25% | 25% | 75% | 25% |
| A+ × A+ | 75% | 0% | 0% | 25% | 75% | 25% |
| O+ × O+ | 0% | 0% | 0% | 100% | 75% | 25% |
| O- × O- | 0% | 0% | 0% | 100% | 0% | 100% |
| AB+ × O+ | 50% | 50% | 0% | 0% | 75% | 25% |
| AB+ × AB+ | 25% | 25% | 50% | 0% | 75% | 25% |
| O+ × A+ | 50% | 0% | 0% | 50% | 75% | 25% |
| A- × A- | 75% | 0% | 0% | 25% | 0% | 100% |
As the predictor computes them, with type A and B parents as AO and BO and Rh+ parents as Dd. The ABO and Rh columns are independent.
How to use this tool
- Choose the ABO type and Rh factor of Parent 1 and Parent 2.
- Read the chance of each child ABO type, the Rh split and the combined ABO and Rh table.
- Check the genotype table and the note on the modeled genotypes before relying on a number.
Frequently asked questions
- Can two type A parents have a type O child?
- Yes, if both carry an O allele (AO). In this model both type A parents are AO, so A+ × A+ gives A at 75% and O at 25%. If either parent is really AA, an O child is not possible.
- What blood type will my baby be if one parent is AB?
- Never O in this model, because an AB parent passes A or B. AB+ × O+ gives A or B at 50% each; AB+ × A+ gives A at 50%, B at 25% and AB at 25%. The Rh split works the same as for any other pair: two Rh+ parents give Rh+ at 75%.
- Can two O parents have a type A child?
- No. Type O passes only the O allele, so O × O gives O at 100%. With two Rh- parents as well, O- × O-, the page reports a certain O- child.
- Can two Rh positive parents have an Rh negative child?
- Yes, if both are Dd. The predictor models Rh+ as Dd, so two Rh+ parents give Rh+ at 75% and Rh- at 25%. If either parent is DD, an Rh- child is not possible.
- Can blood type prove who the father is?
- No. Blood type can only exclude a pairing, never confirm one, and rare types such as the Bombay phenotype and cis-AB can give a child a blood type that looks impossible for the parents, so even an exclusion can be wrong. An A × B couple can have a child of any ABO type, so a child’s type often rules nothing out. Parentage needs a DNA test.
- When does the page show an Rh warning?
- When one parent is Rh- and the other is Rh+, in either order. The risk the note describes applies when the pregnant parent is Rh- and the baby is Rh+: the NHS offers anti-D injections in that case to stop antibodies forming. With both parents Rh+ or both Rh-, the note is not shown.
Related Tools
View all toolsDue Date Calculator
Your due date is the first day of your last period plus 280 days. Enter that date and your cycle length to see it with trimester dates and weeks pregnant.
Child Height Calculator (Mid-Parental)
Mid-parental height calculator: both biological parents’ heights and the child’s sex give Tanner’s target adult height with a range of ± 8.5 cm.
A1C Calculator
A1C calculator: converts A1C to estimated average glucose (eAG) and back in mg/dL or mmol/L with the ADA formula, 28.7 × A1C − 46.7, plus IFCC mmol/mol.
BAC Calculator
Estimate blood alcohol (BAC) from weight in lb or kg, sex, US standard drinks and hours since the first drink. Not a breathalyzer: it cannot clear you to drive.
Blood Donation Recovery Calculator
Enter the date and type of your last blood donation to get your next eligible donation date from Stanford Blood Center rules, plus rough recovery estimates.
Blood Pressure Category Checker
Blood pressure category for one adult reading on the American Heart Association chart. Systolic and diastolic are rated separately; the higher one counts.