Getty Images; Rebecca Zisser/BI

People have long saved for life's biggest milestones: buying a home, getting married, and retirement. Some workers are also putting money aside for something they hope never happens: burnout.Last week, Mary Kane handed in her resignation letter.After six months of feeling exhausted, irritable, and increasingly burned out in her job as a senior marketing manager, the 54-year-old Minnesotan decided she'd had enough.Unlike many workers in a similar position, she wasn't terrified about how she'd pay the bills once she quit. For years, she says, she saved about half of every paycheck, building what she now calls a burnout fund.'Really intentional savings'A burnout fund is a ring-fenced savings pot designed to fund a recovery period, rather than unexpected emergencies such as job loss or medical bills."A burnout fund is really intentional savings where you anticipate needing to take a break," Julie Beckham, Rockland Trust's financial education and development strategy officer, told Business Insider.In that sense, she added, it's an old concept under a new name: "Being intentional in naming any savings account is a good practice."

Sabino Vargas, senior financial advisor at Vanguard, told Business Insider the goal with a burnout fund is to "build enough financial flexibility so you can have choices if a step back or career reset is needed."