To be candid, the superstitions surrounding the black cat are numerous and they either say that they bring bad or good luck in about equal numbers. That’s the power of superstition. Completely irrational but understandable. It is only the human who can harbour these strange beliefs.
However, if you believe that black cats bring good luck the reason may be rooted in ancient and more recent history which has been handed down over the generations to us in the 21st century.
If one crosses your path or enters your house, in Britain more people believe that black cats bring good luck than the opposite. On my research, there are three possible origins for this.

RELATED: Many believe the opposite: When did black cats become bad luck?
Ancient Egypt
In ancient Egypt, the period during which the tamed wildcat became truly domesticated, it was believed that the sacred cat bestowed many blessings in the household that looked after him/her.
The practical blessing that the domestic cat kept down rodent numbers was extended through myth to a more general blessing. I guess you can see how it extended from the working domestic cat being practical and then through superstition doing something much more, bringing good luck.
Inscriptions on ancient tombs tell us that the cat “gives life, prosperity and health every day, and long life and beautiful old age”. And this ancient tradition somehow managed to be passed down through the centuries, even surviving the Christian persecution during the Middle Ages when they believed that cats, and the black cat particularly, where the servants of the devil.
Mediaeval times
Some people feared and hated the cat during these hundreds of years of persecution. Although I shouldn’t generalise because not everybody during the Middle Ages hated or feared cats. There must have been many good people who shunned the notion that the cat was the embodiment of the devil particularly the black cat.
But this fear of the cat meant that if one crossed your path and you survived the experience i.e. the cat did you no harm then that was due to good luck which began the association between cats and good luck. If one came into your home, you could be kind to the cat and appease the devil! This avoided the devil’s wrath. In this extended belief that if you were welcoming to a cat entering your house and you got the devil on your side it brought you good fortune because others might be tormented by the devil but you would not be.
An old British saying
There is an old British saying which goes: “Whenever the cat of the house is black, the lasses of lovers will have no lack.”
The cat is used as a symbol of sexual attraction. The female cat is perhaps the paradigm for females attracting males. The female cat on heat attracts a circle of admiring tomcats. A house with such a cat would be one where the woman will attract a large circle of men.
White cat versus black cat
I’m told that in America the white cat brings luck while the black cat brings bad luck. I welcome comments from American visitors on this. Although it seems that the early settlers to America brought with them the belief that black cats were linked with the devil and were an evil force. The white cat being in direct contrast to the black variety was seen as a force of light against the darkness and thereafter became a symbol of good fortune. As I said, I welcome comments.