What time should I go to bed to wake up feeling refreshed?

We all know how important sleep is. According to scientists, a good night's sleep could be the key to living longer,slimming downand evensnagging a pay rise. But if you lie awake worrying about not getting enough, or wake up feeling groggy despite getting an early night, you're not alone. Find out what time you should really be going to bed and what you can do to make your time in the land of nod count...

How much sleep do I need?

The amount of sleep we need is genetically determined, and varies with age. Up to 5% of the population is 'pre-programmed' to get by on as few as 3 hours sleep a night (famous examples include Winston Churchill and Margaret Thatcher) whilst others need up to 9 hours. However, most of us seem to require about 7 hours in order to function at our best. If you find yourself craving sweets, caffeine and carbohydrates when you wake up, and often catch yourself thinking about sleep during the day, you're probably not getting enough. However, if you wake up without an alarm clock at the same time each day, you're probably on track.

What time should I go to bed?

But it's not all about quantity. Quality counts too. Sleep experts suggest that a 10pm-6am sleep schedule tallies best with our natural circadian rhythms. According to Dr. Matt Walker, head of the Sleep and Neuroimaging Lab at the University of California, Berkeley, "When it comes to bedtime, there's a window of several hours - roughly between 8pm and 12am - during which your brain and body have the opportunity to get all the non-REM and REM shuteye they need to function optimally".

However, if you wake up midway through a sleep cycle, you may still feel tired and groggy, regardless of the number of hours you've spent in dreamland. Why? A good night's sleep consists of 5-6 complete 90 minute sleep cycles for the average adult. Since it takes most people about 15 minutes to fall asleep after going to bed, this means that, if you want to wake up feeling refreshed at 7am, you should go to bed at 9.45pm or 11.15pm. If you're more of a night owl, you might feel more refreshed in the morning if you wait until 12.45am to hop under the covers rather than bedding in at 11.45pm. Befuddled by the maths? Use this onlinesleep calculatorto figure out what time you should be going to bed to wake up with a spring in your step.

What else can I do to ensure I wake up feeling refreshed?

Alternatively, try using theSleep Cycle Alarm Clockapp. This free app uses your smartphone's microphone or accelerometer to monitor your movements and decipher your sleep cycle. Place it near your bed before you go to sleep and it will figure out the optimal time to wake you up within a 30-90 minute window, which you can set before going to bed. It works with both iOS and Android devices, and has won near-universal acclaim from users.

If attempting to fall asleep at a predetermined time sounds too stressful and being woken up early doesn't appeal, why not try a dawn simulation alarm clock?Researchsuggests that dawn simulation may not only enhance mood, but improve athletic and cognitive performance, too. Sold? We thought so.

Lumie Bodyclock Luxe 700, £170, Amazon

Buy now at amazon.co.uk for £170

Read our tips ongetting a better night's sleepandrecovering from a bad night's sleep.