Fill in the details and click Calculate to see your results.
This calculator is also in our free app. Sign in with the same account to keep your history in sync.
A baby inherits one ABO gene and one Rh gene from each parent. Enter both parents' blood groups to see which groups are possible for the baby, which are impossible, and roughly how likely each is.
If the mother is Rh negative and the father Rh positive, the baby may be Rh positive — your doctor will offer anti-D injections to prevent Rh disease in this or a future pregnancy.
| Father's Blood Group | A |
| Father's Rh | Positive (+) |
| Mother's Blood Group | B |
| Mother's Rh | Negative (−) |
| Possible blood groups | AB, A, B, O |
| Not possible | none — all four are possible |
| Rh factor | Rh+ or Rh− (Rh− about 23% chance) |
| Most likely | AB+ (about 25%) |
| Important for pregnancy | Mother Rh− and father Rh+: the baby may be Rh+. Anti-D injections (around 28 weeks and after birth) prevent Rh disease — tell your doctor |
AB, A, B, O.
Try this example →| Father's Blood Group | O |
| Father's Rh | Positive (+) |
| Mother's Blood Group | AB |
| Mother's Rh | Positive (+) |
| Possible blood groups | A, B |
| Not possible | AB, O |
| Rh factor | Rh+ or Rh− (Rh− about 5% chance) |
| Most likely | A+ (about 47%) |
A, B; not AB, O.
Try this example →No. Two O parents can only have an O baby.
No — an AB parent always passes on A or B.
A or O, and Rh positive or (less often) Rh negative.
An Rh-negative mother can make antibodies against an Rh-positive baby's blood; anti-D injections prevent this.