How do I calculate whether I have already hit Coast FIRE?

Coast FIRE asks whether your current investments, left untouched, will compound into your full FIRE number by your chosen retirement age. Work backward: take your future FIRE number, then discount it to today using an assumed real return.

The formula is: Coast number = future FIRE number / (1 + real return) raised to the years remaining. Suppose you want $1.5 million at 65, you are 35 (30 years away), and you assume a 5% real return. You need about $1.5M / (1.05^30) = roughly $347,000 today. If your invested balance already exceeds that, you can technically stop contributing and still coast to the finish. Sensitivity to your return assumption is high, so test a conservative rate too. WealthSerene's FIRE Calculator at wealthserene.com/tools/fire-calculator handles the discounting for you.