A 36-year-old stuck to this one spending rule to help pay off $87,000 of debt in less than a year

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Nyajuok Mangongo, 36, made a handful of moves to pay off $87,000 in credit card debt and a car payment in just under a year.

From picking up weekend hours as a nurse during the pandemic, to buying things from her local Goodwill to resell on eBay and Facebook Marketplace, Mangongo hustled to supplement her income every way she could.

"Anything that I could do that was legal, that was ethical, that was not clashing with my values, I did it to get extra money," Mangongo tells CNBC Select.

But Mangongo didn't just increase her income, she also cut back on her expenses drastically.

Below, we share Mangongo's one spending rule that helped her pay off five-figure debt this year and what you can learn from what she calls a "mindset shift."

When it came to spending during her debt payoff journey, Mangongo limited herself to a maximum of $100 per month on personal expenses. She could allocate this $100 on whatever she wanted, such as a drink out, new earrings, makeup or her Audible book app.

In doing so, Mangongo saved money to use for paying off her debt while also rewarding herself along the way, albeit in little increments. Financial experts agree that while it's crucial to cut back on spending when trying to pay down debt, treating yourself with things here and there keeps you motivated to continue your journey until you reach the big end goal.

As long as the expense doesn't set you back on paying off your debt, it's worth treating yourself. To help you save up for these small rewards along the way, create a separate savings fund in a high-yield account and schedule a small automatic transfer each paycheck (if you have consistent income) so you don't even need to think about it.

By setting a strict monthly budget for herself, Mangongo saved money in addition to learning her priorities.

"Surprisingly, I learned many things we buy are 'wants' not 'needs,'" Mangongo says. "Several months into the journey, I found out that $100 was plenty of money for my personal expenses."

While paying off her debt, Mangongo also used the Dave Ramsey EveryDollar® Budget App to track her spending. The app allows you to separate your expenses into different categories, such as housing, transportation and personal (money for yourself).

Tracking helps you be smarter about how you pay for certain expenses. For example, if it's a transportation category consider paying for those purchases with a credit card that rewards you for spending on gas or travel. For something like a food category, use a card that rewards your grocery shopping.

"Now, I no longer buy things without knowing which categories they belong to," Mangongo says. "Often, I had to think through my purchases such as, is this something that will generate me more money, or something that is taking money away from my wallet?"

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