One account, three tax breaks.

• 2026 IRS limits: $4,400 self-only, $8,750 family, $1,000 catch-up at 55+ (Rev. Proc. 2025-19, IRS Publication 969). Eligibility requires a qualifying high-deductible health plan.
• Both sides start from the same pay before tax. The HSA side assumes every withdrawal pays qualified medical expenses. The taxable side pays income tax (and 7.65% Social Security and Medicare when payroll is on) first, then a simplified yearly tax on growth.
• State treatment differs (for example California and New Jersey). Educational only, not tax advice.
• Every number is hypothetical and depends entirely on what you enter. Small changes in assumptions can change results a lot.
• Returns are smooth and constant in the single-number projection; real returns vary every year, and real markets can do better or worse than anything shown.
• Inflation is a single constant rate you choose (except in historical replays, which use the actual CPI of each year).
• Growth compounds monthly (or at the contribution frequency) and contributions are made at the end of each period.
• No taxes unless you turn on the simplified tax drag (all positive growth taxed each year at your rate, which overstates tax for buy-and-hold). No fees unless you set one.
• Inputs stay in your browser. Saving uses this device's local storage; a share link contains the numbers you entered, so anyone with the link can see them.

Coteau may be wrong. Check every number yourself, and talk to a licensed professional before acting on anything.