The exact time you need to fall asleep tonight to wake up feeling your very best tomorrow.

We’ve all done it: tried to fall asleep at the perfect time to ensure you wake up fresh and ready for that early shift/gym class/hellish presentation meeting with your boss.

We’ve all lain awake, mentally counting how many hours of sleep we are going to get, maybe adding in counting sheep for good measure.

“If I fall asleep RIGHT THIS SECOND… I will get six hours and 26 minutes of sleep. That should do it,” we say to ourselves as we continue to toss and turn.

Well, it turns out we’ve been doing sleep all wrong.

According to a new sleep calculator (which, we’re not entirely sure why, but appears on a UK blinds company website), it’s not about how many hours you’re getting of shut-eye each night at all.

It's all about sleep cycles.

The site uses a "formula" based on the body's "natural rhythms", and all users have to do is enter the time they want to wake up and the calculator will tell you when to head to bed.

And the answers are very, very specific.

Say, for example, you need to wake up at 6:30am. The app suggests bed times of 9:16pm, 10:46pm, 12:16am or 1:46am.

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The Sleep Calculator says each person should pass through five or six sleep cycles - which last roughly 90 minutes - per night.

"Waking up mid-cycle can leave you feeling grumpy and tired, rising in between phases will help you to start the day with a smile on your face," the tool says.

But what about how long it takes to actually fall asleep?

The calculator's done all that for you, too.

"Most people take about 14 minutes to fall asleep and this is factored into your bedtime by this sleep calculator," the website reads.

So heading to bed at 10:46pm means you should be well and truly in The Land of Nod by 11pm, and get a full five sleep cycles in before your alarm starts blaring at 6:30am.

There's even a calculator available for those who are partial to a bit of a daytime snooze, too (cough, guilty, cough).

Just tell the tool you're ready for sleep, and it will tell you the optimum time to get back outside and to work, without that icky, post-nap haze.

Too. Easy.

You can try out the sleep calculator, right here.

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