If you look at several different books on ancient Egypt you may find they all give different dates for when Tutankhamen was Pharaoh, and for most other events in Egyptian history. This page tries to explain why.
Today there are two ways in which we can say when something happened. We can say “It happened after tea on my birthday” or we can say “It happened at 1635 on 11th April.” Most people sometimes use the first way and sometimes the second way. The first way, what we call the relative date, means something only to people who know when your birthday is and what time you have tea; the second way, what we call the absolute date, means something to everyone.
People have counted in days, months and years for thousands of years.
Days are easy: the Sun rises and sets, and a sunset is a very definite ending. So most ancient people ended one day (and so of course started the next) at sunset, as Jews and Moslems and many other people still do. The Jewish Sabbath is on Saturday but it starts at sunset on Friday.
Months are just as easy: the Moon starts as a New Moon, a tiny crescent in the sky just after sunset, then gradually it gets bigger until we have a full moon, then it gets smaller again, and then the cycle starts all over again. The time taken from one New Moon to the next is about thirty days - this is a lunar month. Jews and Moslems and many other people still use lunar months. Our word month comes from moon-th although in Europe today our months do not start on the New Moon.
Years are almost as easy. As we move from Winter into Spring the days get longer and the Sun gets hotter, then Summer follows Spring, and then the days start getting shorter again as we move into Autumn, and the Sun is not so hot, and then Winter follows Autumn. Then the cycle starts all over again. A year is the time taken for the Earth to go round the Sun, and is about three hundred and sixty five days.
The ancient Egyptians started their New Year at the time of the annual flooding of the Nile, but most other ancient people started their New Year at about mid-winter’s day, when the days stopped getting shorter and started getting longer again. Our New Year’s Day on January 1st is a few days after the shortest day of the year.
There is more about the Egyptian Calendar, for adults and children with a serious interest in ancient Egypt, on another page - to link to it click here 
When people in England write the date as 11/04 they mean that it is the eleventh day from the beginning of the fourth month from the beginning of the year - this is an absolute date.
There is more about dates and the calendar, mainly for adults and older children, on other pages of this web site - to link to them please click here
If you want to count years you must start counting from somewhen. Children often use a relative date, counting from the day they were born, that is, their age! But if you want an absolute date, which means something to someone who does not know when you were born, you must start counting from a date which everyone knows about. Today most people in Europe and North America, and many other parts of the world, count the years from the birth of Jesus. Originally only Christians counted the years in this way, so they called the years after Jesus was born AD, which stands for Anno Domini, the Latin for the Year of Our Lord, and the years before Jesus was born they called BC, which stands for Before Christ. Now that lots of non-Christians are using the same numbering system we usually call the years after the birth of Jesus CE for Common Era, and those before the birth of Jesus BCE for Before Common Era - we call it the Common Era because it is the numbering system which everyone has agreed to use. We do not use the letters AD and BC because although Jews and Moslems and many other people are quite happy to count years from the birth of Jesus they do not like using AD and BC because they do not believe that Jesus is Our Lord or that he was the Christ.
There is more about this, mainly for adults and older children, on another page of this web site - to link to it please click here
People who lived before the birth of Jesus could not of course count years BCE! - they all used different ways. The Egyptians counted the years from the year Pharaoh started his reign (what we call Regnal Years) - so they started again every time they had a new Pharaoh!
We now think we know the name of almost every King of Egypt, and the order in which they reigned, but we are not yet certain exactly how long each Pharaoh was King for. So although the Egyptians dated almost everything, converting Regnal Years into absolute dates (years BCE) is very difficult. If for example we think that a certain Pharaoh came to the throne in 1724 (BCE of course! as all dates in ancient Egypt are BCE we do not usually say so) and reigned for eight years, then we can work out that he died in 1716, and so the next Pharaoh came to the throne in 1716. But if then an archaeologist digs up a papyrus dated his Regnal Year 11 then we know that he must have been King for at least eleven years, and so all the dates of all the Pharaohs after him are wrong by at least three years! (If we think we know the absolute date when he died rather than when he became King then it is the date he became Pharaoh that has to be changed, and also therefore the absolute dates for all the Pharaohs who came before him.)
Co-regencies make things even worse. A Pharaoh could not abdicate (stop being Pharaoh), but if he was getting old he might make his son (or the person he had chosen to succeed him) co-regent, to share the responsibility of government with him, so for a time there would be two Pharaohs. The same year could therefore be Regnal Year 35 of one Pharaoh and Regnal Year 6 of another. This means that if we suddenly find a papyrus proving that a Pharaoh who we thought had become Pharaoh when his father died had actually been co-regent with him for twelve years, all the dates of all the Pharaohs before or after them would have to be altered by twelve years.
Archaeologists are always digging up new things in Egypt which tell us more about life in ancient Egypt, and so if one year someone writes a book which says that Tutankhamen reigned from 1336 to 1327, a year later someone else may write another book which gives quite different dates.
This is why serious books on ancient Egypt do not give absolute, BCE, dates, only Regnal Years or the name of the Pharaoh or the number of the dynasty.
For more about dates in ancient Egypt please click here
