You don’t have to look long to find material on how much muscle someone can gain in a month. But did you ever wonder how long it would take to start losing muscle if you took a break from the gym?

“When you stop training, it takes about two weeks to lose that trained state,” says Dr. Thomas O’Connor, aka the “Anabolic Doc,” who makes an appearance in the new Generation Iron 3 film about bodybuilding. “As far as losing muscle tissue, the range is going to be from one week to two weeks. About two weeks.”

O’Connor used his own competitive powerlifting as an example, explaining how he’d lift in 12-week cycles and have a week off at the end of the period.

“After that one week, you are at the peak of gaining and losing [muscle],” O’Connor says. “If you’re just talking about lifting weights, you will hold that muscle for at least a week or two. Based on studies, it’s after a week or two, you’re maxed out and then you start to lose.”

Curious to confirm O’Connor’s range of one to two weeks—leaning toward two—as fact, Muscle & Fitness did a deep dive into the subject and most agree that it takes roughly two weeks to start losing muscle after someone has stopped lifting. A 2015 Danish study from the University of Copenhagen concluded that it takes a physically fit person two weeks without exercise to begin losing muscle.

“Our experiments reveal that inactivity affects the muscular strength in young and older men equally,” says researcher Andreas Vigelsoe of the Center for Healthy Aging and the Department of Biomedical Sciences at the university. “Having had one leg immobilized for two weeks, young people lose up to a third of their muscular strength, while older people lose approximately one-fourth. A young man who is immobilized for two weeks loses muscular strength in his leg equivalent to aging by 40 or 50 years.”

This study was conducted with people who had their legs completely immobilized, so it’s on the extreme end of the rest spectrum (though Science Daily did liken the immobility to taking “a very relaxing holiday”). That being said, the muscle size that was lost so quickly was not easily regained, with researcher Martin Gram concluding, “it’ll take you three times the amount of time you were inactive to regain the muscle mass that you’ve lost.”

Another source, the book Physiology of Sport and Exercise (via Live Strong), says muscle atrophy can begin within a two- to six-week window, giving a slightly longer outlook to size loss. So, one week seems aggressive, but two weeks seems to be the magic number for the starting point. Of course there are variables attached to the two-week starting point for muscle to fade.

“Age is the most important variable,” O’Connor says. “The other variables are going to be what you’re on (supplements/enhancers), what your hormone status is, if you’re sick, if you’re a person that has chronic medical issues and then always, of course, diet and your training regimen.”

Within that, O’Connor adds that someone doing aerobics as their form of fitness could have a different starting point of muscle atrophy in comparison to someone getting his or her exercise from sports or someone who strictly lifts weights in the gym.

But from what Dr. O’Connor says and multiple sources point to, roughly two weeks is the time it would take to start losing muscle if you’d stop hitting the gym.