All over the world, women are doing work they’re not getting paid for.

In rich countries, it might be folding the laundry or staying home to take care of a sick child.

In developing countries, unpaid labor tends to be more physically arduous, like hauling water and chopping wood.

Wherever you are, it’s considered women’s work.

Melinda Gates picked up on this disparity in her travels throughout the world.

Every year, she and her husband, Bill Gates, write a letter outlining their philanthropic priorities. This year, she devoted her portion of the letter to the burdens of unpaid work on women.

"Unless things change, girls today will spend hundreds of thousands more hours than boys doing unpaid work simply because society assumes it’s their responsibility," she writes in the letter, which is written for a teenage audience.

According to the OECD and other sources, women devote more time than men to chores in nearly every country. American women spend more than two hours daily on chores, compared to just 82 minutes for men. Even in Finland, a country that seems more progressive on gender issues, women sweep, scrub, and change diapers for 137 minutes daily, and men do for just 91.

"It ends up robbing women of their potential," Gates said in an interview. "This is a societal issue that in 2016 shouldn't exist anymore."

According to Gates, "globally, women spend an average of 4.5 hours a day on unpaid work. Men spend less than half that much time." The unpaid labor gap is especially large in poor countries. "In India, to take one example, women spend about six hours, and men spend less than one hour," she writes.

And when women are too busy cleaning and cooking, they have less time for paid work. Girls in many countries fall behind in school because they're swamped with tedious chores. Gates writes that reducing women’s unpaid labor from five hours per day to three can increase a country’s female labor-force participation rate by 10 percent. If women participated in the economy at the same levels as men, she writes, global GDP could increase by 12 percent.

The other portion of the letter this year—Bill’s half—concerns the need for new and reliable forms of clean energy. Melinda Gates told me energy can also play a role in fixing the female time-poverty problem, particularly in the developing world. Given all the hours women in developing countries spend collecting water, for example, "if women had access to clean water, it changes everything about their time." She says new types of stoves and other inventions could also help.

At the national level, she recommends stronger family—not "maternity"—leave policies, as well as more resources devoted to women’s health.

Couples should start having conversations about how they can redistribute unpaid chores more fairly, Gates says. That means more American dads pushing vacuum cleaners, and more husbands like one Gates met in Tanzania, who volunteered to help his wife fetch water.

In some cases, men will be better suited to doing these chores because they’re physically stronger. Other times, they’ll have to sacrifice some free time.

"I talked to men in the developing world, and they would say, ‘When I pull water out of the well, it's less labor for me than my wife,’" Gates said. "It does mean sometimes giving up leisure activities, but it means women have time to participate in economy."

As many a sleep-deprived mom can attest, the "redistribution" piece of the puzzle will be hard to accomplish. In the U.S., the gender-chore gap has barely budged in over a decade.

For those who think it can’t be done, Gates offers an example from her personal life. Though Bill and the couples’ children would always help with after-dinner cleanup, she nevertheless was always the last person left in the kitchen, "doing those last few little things."

Finally, she issued an edict: No one leaves the kitchen until mom does.

"Guess what?" she said. "It all got done a lot faster."