Scientists have come up with a formula to enable people to calculate when they are most awake.
Many Britons say are tired during the day
It is CDA + CT + KF = TMT or the time an individual is most tired.
CDA stands for circadian dip in alertness or natural biological rhythms. CT is chronotype or the timing of an individual's biological rhythms.
KF stands for "knacker factors" such as lack of sleep or drinking alcohol. An easy to use formula can be found at www.knackerfactor.co.uk.
The formula was developed by scientists at the fatigue management consultancy AWAKE.
They were commissioned to do the work by the manufacturers of caffeine supplements.
It followed a survey which found that 40% of Britons feel sleepy at work. Over half admitted to making mistakes when tired while 62% claimed tiredness affected their social lives.
The poll also found that men and women experience tiredness differently. Some 64% of women said they become irritable when tired. Men said they make more mistakes.
"Tiredness is an unfortunate reality for many office workers trying to juggle their work, family and social responsibilities," said Dr Paul Jackson, managing director of AWAKE.
"There are situations where we really need to be alert, for example when meeting clients or making important business decisions.
"This simple equation enables anyone to calculate what time of the day they are likely to feel most tired and to schedule their activities accordingly."
But Neil Stanley of the British Sleep Society said people could get the most out of their day by getting a good night's rest.
"It's really quite simple," he told BBC News Online. "If people are tired during the day then they are not getting enough sleep."
He said establishing a proper sleep pattern would help to reduce tiredness during the day.
"If you establish a proper rhythm, your body will make maximum use of that time, whether its six hours or eight hours. It will consolidate sleep."