Your nest egg is the total amount of money you've saved and invested to support yourself in retirement—the financial cushion you've built over your working years that you'll rely on when employment income stops. It typically includes retirement accounts like 401(k)s and IRAs, personal savings and investments, and sometimes home equity or other assets you plan to convert to cash.

The term "nest egg" comes from the practice of leaving a fake egg in a hen's nest to encourage her to keep laying—the idea being that a starter amount encourages continued saving and growth. Your retirement nest egg works similarly: starting early and consistently adding to it, even in small amounts, helps it grow substantially over time through compound returns. A nest egg that's been growing for 30 or 40 years can be dramatically larger than the sum of what you contributed, thanks to investment returns compounding year after year.

The challenge isn't just building your nest egg—it's also making it last throughout retirement. You need to accumulate enough during your working years, invest it appropriately for growth and protection, manage withdrawals carefully so you don't deplete it too quickly, and protect it from inflation, market downturns, and unexpected expenses. Financial advisors often suggest various rules of thumb for nest egg adequacy—like having 10-12 times your final salary saved by retirement, or enough to safely withdraw 4% annually—but the right size depends on your specific retirement lifestyle, other income sources, and life expectancy.