In December, Americans were holding on to hundreds of millions of days of unused paid time off, referred to as PTO.

By the end of the month, many of those days vanished, just as they do every year when use-it-or-lose-it balances reset.

This year can be different.

"The bottom line is, take a vacation if you can," wrote Allina Health psychologist Dr. Kathryn Isham. "When you take time away from the stresses of work and daily life, it can improve our physical and mental health, motivation, relationships, job performance and perspective."

Nearly half of all U.S. workers who have PTO do not take all of it in a year, according to a recent Pew survey. Most said they either don't feel they need to take more time or they worry about falling behind at work.

Meanwhile, employee burnout rates continue to rise, and two-thirds of workers Aflac surveyed last year said more time off is the preferred antidote.

Studies have shown positive health outcomes associated with taking more vacations, including a reduced risk of heart attacks and lower incidences of depression.

And despite fears of recovering from vacation brain fog, well-rested employees tend to perform better and end up sticking around longer. An Ernst & Young survey found that for every 10 additional hours its employees took off in a year, performance ratings rose 8%.

About 90% of full-time, private-sector employees have access to paid vacation time, according to the U.S. Bureau of Labor Statistics, but less than half of part-time staffers do. As employers continue to hurt for help, many have boosted time-off benefits to lure workers. New laws have also established a minimum amount of earned paid leave in Minnesota.

For those with a PTO balance to spend down this year, January is the time to plan. Here are some pointers to make the most of your time and use it all before you let it go to waste:

Maximize holidays

The typical "life hack" offered on social media and travel blogs is to plan vacations around federal holidays because they are days you might already be off work. You can make long weekends even longer, often without sacrificing additional PTO. An online calendar, holidays-optimizer.org, can help maximize time off around holidays.

"Even if you can't take advantage of each public holiday to maximize your time off, you'd still be surprised by how much you can benefit from a few well-timed vacation requests," according to personal finance blog the Points Guy.

For example, Memorial Day is Monday, May 27 this year. You could ask off for Friday, May 24 or Tuesday, May 28 to give yourself a four-day break by using just one PTO day.

Check to figure out how your employer handles PTO. Are holidays and sick time separate pools? Or is PTO inclusive of everything? In the latter case, you'd have to use two days of PTO in the Memorial Day example.

Also around holidays, your co-workers might want time off, too, meaning you might have competition and should put your request in early. Those times are also when travel costs could be highest, if you were planning to take a trip.

Embrace the staycation

A vacation doesn't have to cost anything, if that has been a deciding factor in planning time away from work. A "staycation" can be as simple as spending time at home catching up on reading, gardening or other hobbies. Or it can involve booking a spa day, a nice dinner and maybe even a night at a hotel while a babysitter watches the kids.

"The beauty of a staycation is that you can tailor its purpose to your needs," AAA says.

Just planning a vacation/staycation can boost happiness weeks in advance as the anticipation lowers stress.

"Conversely, if stress hormones stay chronically elevated due to lack of rest and recovery time that comes as a result of putting off or forgoing vacation, you will be more susceptible to not only colds or the flu but also vulnerable longer term to more serious illnesses like heart disease or cancer," according to the Harvard Business Review.

Prioritize mental health

Sometimes a random day off is all it takes to cool down the burnout, and some workplaces have even added "mental health days" that employees can take specifically to unwind.

Maybe you want to pull your kid out of school, too, and go to a matinee movie. Maybe you just want to sleep in or read a book on your patio. As long as you don't use these days to wallow in self-pity or mindlessly scroll social media, you're doing it right.

"Be intentional about the activities you do during a mental health day to get the full benefits and improve your health," Mayo Clinic said.

Saving for sickness?

For jobs that provide a single pool of PTO, there might be some pressure to hold on to those precious hours in case of emergencies.

This is especially essential in preparing for cold and flu season at the end of the year. But if the bugs brought home from your child's day care aren't as severe this time around, you could be leaving PTO on the table.

It might help to be flexible with late-season holidays like Thanksgiving and Christmas. If you were only taking a few days off for Turkey Day but have lots of PTO to spend because you stayed healthy, consider taking the whole week off instead. Same goes for the last week of the year or perhaps an early December respite to prepare for the holiday rush. Talk to your manager well in advance if this is a possibility.

For those with separate banks of paid time off, try not to use vacation days for sick days if possible in order to maximize intentional time away. The best defense against illness might be some preventive R&R.

Not just desk jobs

Much PTO advice focuses on white-collar employees with predictable 40-hour workweeks. But millions of Americans are self-employed, and millions more work in the service industry and health care professions with atypical hours and seasonal intensity.

The broad consensus for all of those fields is to plan well in advance, as far out as your employer allows. Child-care providers might include a personal week off in their schedule when releasing yearly calendars for families to follow, for example. Nurses should know their policies, ask well in advance and keep close tabs on their PTO balances, nurse advocate Kylee Nelson wrote.

Farmers and construction workers who have demanding seasonal schedules can make plans for the quiet times. Business owners can also plan ahead for slowdowns.

Other paid leave

Talk to your boss, HR department or union rep about paid leave you might have beyond vacation and sick days. This can include those aforementioned mental health/wellness days, parental leave, bereavement, paid time to volunteer and other specific benefits. Many employers also offer a PTO donation policy, which can help colleagues cover unexpected emergencies and help you use days that will otherwise expire.

Some employers also offer income protection, which can house any unused PTO at the end of the year. That way those past forfeited days could help you collect your full pay for longer if you end up on short-term disability following a major injury.

Managers should encourage workers to take their vacations to promote a healthy workforce, workplace experts said. Some employers have even started mandating the use of PTO as many Americans remain resistant to taking "too much" time away.

"If your company offers open leave or allows employees to roll over unused vacation days, emphasizing the benefits of regular annual vacations can help promote the practice," says the Society of Human Resources Management.