What should I do with a year-end bonus or a financial windfall?

Slow down and give every dollar a job before it disappears into lifestyle spending. A practical order: first, top off your emergency fund to 3–6 months of expenses; next, knock out high-interest debt like credit cards; then max out tax-advantaged accounts such as your 401(k), IRA, or HSA for the year. After that, invest the rest in a diversified, low-cost portfolio toward long-term goals. Remember a cash bonus is taxed as ordinary income (and often withheld at a flat 22% federal supplemental rate), so don't spend the gross. It's fine to carve off a small slice – say 5–10% – for something fun so the plan feels rewarding. Run the numbers at wealthserene.com/tools/opportunity-cost to see what investing the rest could grow into.