Are you a lark or an owl? Are you at your best early in the morning or late at night?
Many people have difficulty getting up early
Whatever the answer, scientists believe they may now know why some of us are early risers while others prefer to burn the midnight oil.
The answer appears to lie in our genes.
Researchers at the University of Surrey say they have found a link between people's preference for mornings or evenings and a gene called Period 3.
This gene is one of those involved in regulating the body's internal clock. It comes in two forms - a shorter and longer one.
'Long and short of it'
Researchers have found that people with an extreme preference for early mornings are more likely to have a long version of Period 3.
In contrast, those with an extreme preference for evenings are more likely to have the shorter version.
Your day or night preference is obviously a complex behavioural trait. It is not solely down to one single gene
The findings are based on tests carried out on almost 500 people who recently visited London's Science Museum.
Researchers took samples from the cheeks of each of these people and analysed their DNA.
They also asked them to fill out questionnaires to determine whether they are morning or evening people, by asking them when they liked to exercise and how difficult they found it to wake up.
The researchers compared the results from the DNA tests to those from the questionnaires.
"We found most of the extreme morning preference people have the longer gene and the extreme evening preference people have the short gene," Dr Simon Archer, who led the study told the BBC.
"There are extreme morning people and extreme evening people and it seems that behaviour has a genetic basis to it."
Dr Archer said despite the findings, other genes and other factors also played an important role in determining who among us are larks and who are owls.
"Your day or night preference is obviously a complex behavioural trait. It is not solely down to one single gene.
"It is a combination of genes that interact together to form your body clock," he said
"But, of course, there is an influence from your lifestyle. It is not all to do with your genetics. You can chose to follow a particular life pattern. You can override your genes."
Dr Archer suggested the findings could have practical advantages for some people.
For instance, people with short versions of the gene may prefer to work nightshifts while those with long versions may prefer to opt for early starts.
"In our current society, where people are working more around the clock it is probably an advantage to certain people to be able to get up early in the morning," he said.
The study is published in Sleep, the journal of the American Academy of Sleep Medicine and the Sleep Research Society.