latte factor
n. Seemingly insignificant daily purchases that add up to a significant amount of money over time.
The advisor also suggested that they carefully watch their spending on little things — such as buying a cup of coffee every day.

"You get a mocha at Starbucks and it costs $3. You buy a biscuit for $1.50. At work, you get a diet Coke and Snickers. Before you know it, you've spent $10 a day," Holt said. "It's the latte factor."
—Deborah Adamson, “Money makeover,” The Honolulu Advertiser, October 19, 2003
Trimming a dollar here and there translates into big savings at the end of the year, these women say.

That's the latte factor, says Betty Neal, certified financial planner and investment representative for Edward Jones.

The latte factor is unconscious day-to-day frivolous spending such as buying a daily latte.
—Juliana Goodwin, “Sticking to a budget is key to financial freedom,” Springfield News-Leader (Springfield, MO), April 08, 2003
1999 (earliest)
"Everybody is always tight," he said. "Saving has nothing to do with income and everything to do with lifestyle."

Bach calls it the "latte factor." He described a 22-year-old woman who insisted she couldn't afford to save. But she discovered she was spending about $10 a day on coffee and snacks.

If she cuts down enough to save $2,000 a year and invests the money at 11 percent, she would have $2 million by the time she retired.
—Jilian Mincer, “He knows firsthand: Spenders can become savers,” The Kansas City Star, May 02, 1999
The phrase latte factor was coined by financial analyst and investment guru David Bach, author of the bestselling book, The Automatic Millionaire. In fact, Bach, via his company FinishRich, has a trademark on the term "Latte Factor," which refers to "educational seminars and workshops in the field of investment and financial planning."