If you want to spend money wisely, consider paying someone to do your laundry or grocery shopping.

Eliminating stressful things from your to-do list frees up time for more meaningful activities, like spending time with family or friends, which can lead to more happiness.

That's according to a Harvard Business School professor, who says that many of us ignore this simple way to be happier because spending the money makes us feel guilty.

We all want more time to spend doing things we enjoy.

But according to Harvard Business School professor Ashley Whillans, we aren't doing the one thing that can afford us more time: Spending money to eliminate our most stressful daily or weekly tasks.

During a podcast with the Harvard Business Review's Curt Nickisch, Whillans says exchanging money for more free time can make us happier. Specifically, "using money to buy ourselves out of negative experiences," like washing and folding laundry or cleaning house.

For Whillans, its opting for a pricier apartment close to work, where everything is within walking distance and there's no tedious commute, she said. Whillans' research shows that "buying time" in this way leads to greater happiness and less stress. But often, something is holding us back.

"I find in my studies that people feel really guilty about outsourcing even though they're giving up money to have more time that they've earned," Whillans said.

Paying someone to deliver meals, wash and fold our laundry, or mow the lawn makes us feel like a burden, she said. We also feel like it shows others we're not capable of doing our own chores.

The best way to counteract those feelings of guilt, Whillans said, is to focus on the value you're gaining. The key to ensuring that free time leads to greater happiness is to make it meaningful, she said.

Read more: A Harvard professor says most of us squander 5-minute opportunities to be happier every day

"Just the simple act of thinking about giving up money to have more free time seems to make people plan their time a little bit better. If I’m going to incur this cost to have this free time, then I’m going make sure I really enjoy the free time that I have," Whillans said.

Whenever we open our wallet, she argues, we should be asking ourselves "Is this money changing the way that I spend my time?"