Can two parents without red hair have a red-haired baby?

Yes, if both carry a red version of the MC1R gene. In the simple model, each of their children then has a 1 in 4 chance of red hair.

Does red hair skip a generation?

It can look that way. Red hair is usually recessive, so the red version can pass quietly through parents and grandparents with brown or blond hair, then show up again in a child.

How can I tell if I carry the red hair gene?

Not from your own hair. Red hair in close relatives is the best clue. If your mother or father has red hair and you do not, the simple model says you carry one red copy.

We already have a dark-haired child. Does that change the odds for the next one?

No. The chances apply to each pregnancy separately, so two carrier parents have the same 1 in 4 chance of a red-haired child every time.

How common is red hair?

In UK Biobank, a large study of adults of white British ancestry, 4.6% said red was their natural hair colour, about 1 in 22. The English version of the calculator uses this UK figure: it assumes a parent without red hair carries a red version 1 time in 3.

Red-haired baby, no red-haired parents: how it happens

Yes, if both of you carry the red version

Red hair comes mainly from one gene, MC1R, and it is usually inherited as a recessive trait. In most cases a child needs a red version of the gene from both biological parents to have red hair. A parent with one red copy and one ordinary copy usually has no red hair at all, yet can pass the red copy on.

So two parents with brown, black or blond hair can have a red-haired baby if both carry a red version. In the simple model, each of their children then has a 1 in 4 chance of red hair.

What MC1R does

MC1R holds the instructions for a receptor that sits mainly on pigment cells. That receptor decides which kind of melanin the cells make: eumelanin, which is dark, or pheomelanin, which is red to yellow. When the receptor does not work, the cells make mostly pheomelanin. People who make mostly pheomelanin tend to have red or blond hair, freckles and fair skin that tans poorly.

The link to red hair was reported in 1995. Researchers found changes in MC1R in more than 80% of people with red hair or fair skin that tans poorly, but in fewer than 20% of people with brown or black hair.

The 1 in 4 chance, worked out

Everyone has two copies of MC1R and passes one of them, at random, to each child. A carrier passes on the red version half of the time.

When both of you are carriers, each child has:

a 1 in 4 chance of getting the red version from both of you, and red hair;
a 2 in 4 chance of getting one red version, and being a carrier like you;
a 1 in 4 chance of getting no red version at all.

These chances apply to each pregnancy separately. Two dark-haired children do not make a red-haired third more or less likely.

Why red hair seems to skip generations

Because carriers usually show no red, the red version can travel quietly through parents and grandparents with dark or blond hair. It only shows when two carriers have a child who gets both red copies. To a family, that looks like red hair skipping one or more generations.

Carriers are not always completely invisible, though. A single switched-off copy of MC1R can give strawberry blond or auburn hair. A study of families with many redheads also found evidence that one copy can affect beard colour, skin type and freckling. So a reddish beard or plenty of freckles can be a hint, but brown hair and no freckles do not rule anything out.

How common carriers are

Red versions of MC1R are common in some populations. In UK Biobank, a large study of adults of white British ancestry, 4.6% said red was their natural hair colour, and about 92% of them carried two MC1R variants. The two most common strong red versions of the gene were each found on roughly 1 in 10 copies of MC1R in UK genetic data. That is why so many people with brown or blond hair carry one without ever knowing it.

How to use the calculator

The baby hair colour calculator above cannot see your genes, so it uses the average for the population it is written for. On these English pages it assumes a parent without red hair carries the red version 1 time in 3, which fits the 4.6% of red-haired adults in UK Biobank. Red hair is rarer in continental Europe, so the other language versions of the calculator use lower figures, from 1 in 4 in the Netherlands to 1 in 6 in Spain and Italy.

Red hair in the family is the best clue you have. For each parent who has redheads among their parents, brothers or sisters, grandparents, aunts, uncles or cousins, tick "Someone in their family has red hair". The calculator then raises that parent's chance of being a carrier to 1 in 2.

For two dark-haired parents, that gives:

neither box ticked: about a 1% chance of red hair;
one box ticked: about 2.5%;
both boxes ticked: about 6%.

If each of you has a red-haired mother or father, the simple model says you are both carriers for certain, and the chance is the full 1 in 4. That is higher than the calculator shows, because its box covers any relative, not just a parent.

When one of you already has red hair, the model assumes the red-haired parent always passes on a red version, so the chance depends only on the other parent. See one dark-haired and one red-haired parent and two red-haired parents.

The limits of the simple model

Real genetics is messier than one gene with two versions. Some versions of MC1R have a strong effect and others only a mild one. In UK Biobank, most people with two MC1R variants had blond or light brown hair rather than red, and MC1R explained only part of the genetic influence on red hair. Other genes play a role too, and many genes shape the exact shade.

So treat the calculator's figures as a fun estimate of the odds, not a genetic test. They are odds, not promises, and families have a way of surprising everyone.