How do I figure out my Coast FIRE number for my current age?

Your Coast FIRE number is the amount you'd need invested today so that compound growth alone reaches your full FIRE target by your chosen retirement age — no further contributions required. Work backward: take your full number (say $1.5 million at 65), then discount it by your expected real return over the years remaining. At about 5% real growth, money roughly doubles every 14 years, so a 37-year-old with 28 years to 65 needs only around $375,000 today to coast to $1.5 million. The younger you are, the smaller the Coast number, because time does the heavy lifting. Once you hit it, you can stop saving for retirement and only earn enough to cover current bills. Be conservative with the assumed return so you're not relying on a perfect market. Calculate yours at wealthserene.com/tools/fire-calculator.