How long does it take a chicken to lay fertilized egg?

It's important to clarify that a chicken doesn't lay a "fertilized egg" in the same way a human might have a fertilized egg. Here's why:

* Chickens lay eggs regardless of fertilization: Chickens are designed to lay eggs as part of their natural cycle, whether or not they've mated with a rooster. These eggs are unfertilized and will not hatch into chicks.

* Fertilization happens during mating: If a rooster mates with a hen, the rooster's sperm can fertilize the egg inside the hen. This occurs within a short timeframe after mating.

* Development of a chick: If the egg is fertilized, the chick begins to develop inside the egg. This takes approximately 21 days from the time the egg is laid.

So, the answer to your question is: It takes 21 days for a fertilized chicken egg to hatch into a chick.