The answer is harder than you think.

According to experts, it primarily boils down to just how tired you are. To make the best decision, you need to assess your recent sleep history and determine whether you’re merely feeling sluggish or you’re woefully sleep-deprived. Here’s what to do.

Obviously, both sleep and exercise are vital, and ideally, adults should make time for both. “Sleep is a pillar of health,” says Dr. Phyllis Zee, chief of sleep medicine at Northwestern University Feinberg School of Medicine. “Getting the recommended seven hours a night is important for metabolic function, weight regulation, and [brain health]. An inadequate amount or quality of sleep is associated with both short and long-term poor health measures, increasing the risk for heart disease, memory problems, and diabetes.”

Consistent physical exercise yields similar benefits and, just like not getting enough sleep, failing to exercise can have serious health consequences. Not only that, but “there is a bidirectional relationship between sleep quality and physical activity,” Zee says. “Exercise can improve deep sleep, and sleeping better enhances the ability to exercise the next day.”

Because both are so critical for optimum health, medical experts hesitate to say one is more important than the other. However, there is a key differentiator between the two: “We have a biological need to sleep — it’s a behavior we must do every day,” says Christopher Kline, Ph.D., an assistant professor at the University of Pittsburgh’s Physical Activity and Weight Management Research Center. “Physical activity, on the other hand, is definitely beneficial for health, but being less active for a few days here and there doesn’t have the same negative health impact as skimping on sleep for consecutive days.”

In other words, skipping workouts, while not ideal, won’t stop you from operating, whereas being sleep deprived definitely will. “Sleep deprivation can impact many aspects of daytime function, including how parents interact and deal with their children,” Kline says. “Too little sleep or poor-quality sleep can impact mood, make you more volatile, and increase anxiety and depression symptoms.”

If you’re really sleep-deprived, meaning you’ve slept too few hours or slept poorly for consecutive nights, you should choose more sleep. Otherwise, exercise is the best choice.

“Thirty minutes of exercise is more impactful health-wise than 30 minutes of extra sleep,” Kline says. “However, that’s only if you are getting the basal amount of your necessary sleep need, meaning at least 6.5 or 7 hours a night. So, if you get, say, seven hours, so you’re at the lower end of the healthy range, then I’d definitely say exercise instead of moving to from seven to 7.5 hours of sleep.”

If your extra sleep comes in the form of a nap, there’s a caveat: Keep it short:

“Research shows that power naps of 30 minutes or less can result in a significant increase in energy and alertness,” Kline says. “And because you’re not getting into the deepest stages of sleep, a short nap won’t impair the following night’s sleep like a longer nap will. The problem, though, is if you are sleep deprived, it’s difficult to stop that nap at 30 minutes. Longer naps and those placed later in the day, such as at 2 or 3 p.m., set forth a vicious cycle of sleeping terribly that night, then needing a nap the next day, then sleeping terribly again the next night.”

Zee agrees that the decision to snooze or exercise depends on your tiredness level. If you got a decent amount sleep the night before but have just hit a midday energy slump, then don’t nap, she says. Instead, take a 30-minute walk or do some other form of exercise, which will also help you sleep better and deeper that night.

And when it comes to those early-morning hours that could either be spent in bed or used to bust a sweat: “If you are awake, it’s past 5 a.m., and you can’t fall back asleep, get up,” Zee says. “Again, this will help you fall asleep earlier and stay asleep longer that coming night.”

In order to stay somewhat active without sacrificing sleep, the trick may be to look for non-traditional ways to get physical activity. While you may not score enough alone time to do a solid weight-training session or a 30-mile bike ride, there are countless ways to sneak in extra movement throughout the day. Mowing the lawn, vacuuming, dancing around the kitchen with the baby in your arms, strapping the kid in their stroller and going for a quick jog—it all counts, and none of it requires skipping sleep.