How this estimate is built

• You can either find the earliest date your numbers support, or check a specific date you already have in mind — both run the same simulation, just searching for a date versus testing one.
• Balances compound monthly at the return rates you entered; contributions stop the month you quit. IRA and 401(k) contributions are entered as annual totals; brokerage and HYSA contributions are entered as monthly amounts. The current calendar month is prorated by the days remaining, so partial-month growth and contributions aren't overcounted.
• Required Minimum Distributions kick in automatically once you reach RMD age (73 if born 1951–1959, 75 if born 1960 or later, per SECURE 2.0), using the IRS Uniform Lifetime Table. The forced amount moves from your IRA/401(k) into HYSA whether or not you need it that year — the IRA has no exception for still working, but the 401(k) does, so it only applies once you've actually left that employer.
• A monthly health insurance cost before Medicare (65) can be added to model COBRA or marketplace coverage during early retirement — it's added on top of your regular living expenses and disappears automatically at 65, when Medicare is assumed to already be baked into your normal spending.
• Each major expense can be assigned its own funding account ("Pay from") instead of following your general withdrawal strategy — useful for money you're already earmarking for a specific purchase. If the designated account can't fully cover it (not eligible yet, or insufficient balance), the shortfall falls back to your general withdrawal order.
• Major expenses and windfalls are funded from savings the moment they occur — even in years you're still working, drawing from HYSA and brokerage (and IRA if you're 59½ or older). Your regular living expenses aren't included in that pre-retirement draw, since your paycheck is assumed to cover those until you quit.
• Withdrawals are drawn in this order: HYSA, then brokerage, then 401(k), then IRA — unless you check "Preserve my HYSA as an emergency fund," which flips the order to 401(k), then brokerage, then IRA, then HYSA last. Either way, this is a simplifying assumption, not tax advice — a real drawdown order depends on your tax bracket and account rules.
• Your monthly living expenses grow each year with the inflation rate you set; one-time expenses and income are applied in the calendar year you assign them.
• Social Security is assumed to receive the same cost-of-living adjustment as your inflation rate, starting the month you reach the age you specify. Pension income is assumed flat, with no COLA, since most private pensions don't adjust for inflation — edit the number yourself in future years if yours does.
• The projection runs through the December you turn 95. If any year's needs exceed every account's balance plus Social Security, pension, and part-time income, that quit date is marked infeasible.
• The 401(k) is treated as off-limits until you've actually quit this employer AND you're either 59½ or, with "Use the Rule of 55" checked, at least 55 as of January 1 of that year (Rule of 55 requires separation from service, so it can't apply while you're still working there). The IRA has no such employment condition, just the standard 59½ age gate. If a need can't be covered by eligible accounts, the plan is marked infeasible for that date. This is a simplifying model of real IRS rules, not tax advice — confirm your specific eligibility with a professional.
• If you set an "expected effective tax rate," 401(k), IRA, and RMD withdrawals are grossed up so the after-tax amount actually covers your spending need — HYSA and brokerage withdrawals aren't grossed up, since typically only interest or gains are taxed there, not the full withdrawal. This uses one flat rate for simplicity; it doesn't model progressive tax brackets, the taxability of Social Security, or capital gains treatment. Leave it at 0% to see pre-tax figures only, and treat any nonzero result as a rough planning estimate, not a tax projection.