The simple thing that helped me save $30,000

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What's the secret to saving thousands of dollars in a relatively short period of time? The answer might be a lot simpler than you think.

Luis Renteria managed to save more than $30,000 in three years. He didn't win any money or force himself to stay home every night. The solution, for him, was just to manage his money very carefully. And he credits one really simply tool: a spreadsheet.

Every credit card swipe, dollar earned, and bill paid is meticulously tracked and accounted for on the budget he created using an Excel spreadsheet.

"I look at my budget five times a day, and edit it at least five times a day, " said Renteria, who works full time in IT.

The budget is even color coded to denote different categories, and includes saving balances and targets.

Related: 6 painless ways to save thousands

Renteria has always been a planner. Every major life decision he makes is carefully researched and planned out.

"I grew up poor," said Renteria, 32, who was raised by a single mother. As a young boy he remembers seeing her sitting on the floor surrounded by bills. "She was trying to make sense of her finances and how we were going to stay in the apartment we were in and have food."

That image has stuck with him and motivated him to be financially savvy.

"From a young age, I understood the importance of money. Not that money was everything, but not having it was."

When Renteria was in high school, a college adviser came to his house to discuss his financial aid options, but the idea of taking on so much debt weighed heavily on him.

"I saw the whole conversation as a practice in getting me to take on debt, and that didn't sound right at the time," he said. "I knew it wasn't what I wanted."

So he explored his options and joined the Navy at age 19. He wanted to serve his country, but he also liked the idea of gaining applicable job training and resume-building skills.

In 2009, he headed back home to Houston, but only after spending a lot of time researching the local employment situation, cost of living and housing affordability.

"My plan was to use the job experience I got, and even though I left at the height of the recession, I was still able to get a job."

Related: How we saved $40,000 to travel the world for a year...and never came back

He decided to live with his mom to save money, and used his military benefits to get his college degree -- debt free.

During the three years he lived at home he also worked and went to school full time. It was during this period when he set up a budget and was able to save $30,000.

Then in 2013, after much research on prices, interest rates and location, Renteria bought his own home a year before graduation: a three-bedroom, two bath home for $136,000.

Although he used a VA loan, which doesn't require a down payment, he stuck to a price range where he would have been able to afford to put 20% down.

While he had budgeted for the cost of owning a new home, the purchase still left him feeling money was tight. "I was doing okay but not great, and knew that I could better."

For first budget, he'd been following general personal finance guidelines like the 50/20/30 rule that calls for half of your income to cover essentials, 20% to go to savings and financial goals and 30% for flexible spending.

But after the home purchase, he stepped up his budget game and put the accounting skills he learned in college to use.

"I decided to treat my finances like a business treats its cash flow. They don't operate on general principles, they operate in the detail and the minute," he said.

Related: This 28-year-old saw every country in the world ... on a shoestring budget

This melding of practices led to the creation of the spreadsheet he currently uses that tracks every penny coming in and out.

"It has been like night and day," he said of the difference between his two budgeting practices.

The new budget has helped him better understand his cash flow and spending habits, and he hopes to one day have enough saved that he could -- if necessary -- pay off his entire mortgage.

"It comes back to me being that child -- watching my mother struggle."

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