Waking up from a refreshing nap feels great. You’re no longer exhausted, have more energy and can focus on what you need to get done. The problem is that not every nap falls into this category. Sometimes our naps last too long, leaving us disoriented when we wake up and somehow even more tired than before. If it sounds like figuring out the perfect nap is a science, that’s because it is. The benefits of a nap are highly dependent on how long you sleep. Here’s a breakdown of what happens to your brain during naps of different lengths.

10 minutes: Believe it or not, even just a 10-minute nap can make a big difference. According to a study published in the journal Sleep, researchers found that snoozing for 10 minutes can immediately increase alertness and boost cognitive performance for as long as three hours.

20 minutes: The National Sleep Foundation says that 20 minutes is an ideal nap length, allowing you to reap benefits like improved alertness, enhanced performance and being in a better mood.

60 minutes:  If you are able to sleep for a full hour in the afternoon, you may be less impulsive and more tolerant of frustration. The only problem is that if you nap more than 30 minutes during the day, it may disrupt your sleep later that night.

90 minutes: Though a 90-minute nap is usually too long, that’s not necessarily the case if your sleep was severely disrupted the night before. Having said that, napping for an hour and a half can provide the same cognitive benefits as an eight-hour sleep period. On top of that, a 90-minute nap can boost your creativity.

While you’re planning your nap, don’t forget to time it during the right time of day dependent on your activity schedule. You may also want to time your caffeine intake with your naps to maximize the benefits.