How do I estimate what health insurance will cost me if I retire at 45 before Medicare?

Before Medicare at 65, most early retirees buy an individual plan on the Affordable Care Act marketplace at healthcare.gov or their state exchange. The sticker premium for a mid-tier plan can easily run several hundred to over a thousand dollars a month per person, but the number that matters is your net premium after subsidies, which is tied to your household income (MAGI), not your net worth. A FIRE'd 45-year-old with modest taxable income can often qualify for large premium tax credits, sometimes bringing net premiums very low. Budget for the full picture: premiums plus deductibles and out-of-pocket maximums, which can each be several thousand dollars. Because subsidies depend on income you can partly control, health-insurance planning and tax planning are intertwined in early retirement. Run the numbers annually since ACA rules and subsidy thresholds change.