How ChartFI models your money

You are financially independent in the first year that your portfolio × your safe withdrawal rate (SWR) ≥ your annual expenses. Two numbers fall out of that and appear throughout the app:

• FI Number = your annual expenses ÷ SWR. At a 4% SWR, $100k of spending needs a $2.5M portfolio.
• FI Year = the first calendar year your projected portfolio reaches that target.

Spending is organized around five life phases — Working, Wind-down, Early retirement, Retired and Downsized — because the budget differs in each. The last three require you to have actually retired: turning 65 is a health-coverage fact, not a work fact, so a plan that works to 70 keeps contributing and keeps its working budget until then. Downsized needs both triggers — retired and past your downsize year.

Tax planning segments on different boundaries, because the tax rules change at ages the budget does not care about: the 10% early-withdrawal penalty before 59½, the ACA gap between retiring and Medicare, Medicare from 65, and RMDs from 73. The Roth-conversion optimizer sizes a separate conversion target in each of those bands.

Taxes are where a FIRE plan is won or lost, so this is where ChartFI spends most of its effort. Each projection year computes taxes from your actual income sources and account types, not a flat effective rate:

The constants ship for the current tax year and are the same for every plan — they are not a per-plan setting. Like any model of the tax code, they are an approximation that improves as the rules are updated.

Your FI Year on the projection assumes steady, average returns every year. Real markets deliver good and bad years in an unlucky order (“sequence-of-returns risk”). The Monte Carlo analysis runs hundreds of alternate lifetimes for your exact plan and reports the share in which your plan always met its spending needs (the success rate), the range of portfolio outcomes (the fan chart), and how much your FI date moves with luck.

On top of the fan chart you can overlay named historical scenario lines — a deterministic replay of your exact plan through real cohorts such as the Great Depression (1929), the 1966 stagflation retiree, the 2000 dot-com-and-GFC lost decade, and the 1982 bull market — each using that era's actual returns and inflation. The underlying return data comes from public sources (Damodaran / NYU Stern for stocks, bonds, cash and inflation; Nareit for REITs).

The honest limit hasn't moved: every mode still rests on a finite return history and on assumptions you can only estimate, so read the success rate as a stress-test of your plan's resilience, not a probability of the future. The right use is to push returns, volatility, inflation, or withdrawal rate to a pessimistic case and watch how far the FI Year slips.

The calculation engine is snapshot-tested across more than 80 household scenarios — every field of every projection year is pinned to a reviewed expected value, so a code change that alters any number is caught before it ships. On top of that, each run applies validation and reconciliation checks that flag internal inconsistencies (for example, cash identities that don't balance) so a plan that clears them is internally coherent.

What that buys you is consistency — the model computes what it says it computes, the same way every time. It does not, and cannot, promise the market will cooperate.

• No accuracy percentages or guarantees. We don't publish an “X% accurate” figure, because no honest projection can. A projection is an estimate from stated assumptions.
• No account aggregation. ChartFI doesn't link to your bank or brokerage; you enter balances and, once a year, real year-end numbers in Plan vs Actual. That's a deliberate privacy trade-off.
• Capital gains use average cost basis, and start from the cost basis you enter. Selling shares from a taxable account to fund spending realizes capital gain on the appreciation above your cost basis, at the account's average — there are no individual tax lots, so specific-lot selection and tax-loss harvesting aren't modeled, and every gain is treated as long-term. If you don't enter a cost basis for an account, the plan assumes the balance you typed is entirely basis and taxes only the growth it projects from there, which understates the tax on holdings you have owned for a long time. Dividends and yield are taxed every year as they accrue.
• It isn't financial, tax, or legal advice. It's a planning tool. Big, irreversible moves — large Roth conversions, claiming decisions — are worth checking with a professional who knows your full situation.

An honest, updatable comparison. Every tool here is good at something; the right choice depends on what you value. Where a competitor is stronger, we say so.

The short version: ChartFI's edge is the guidance loop and tax-timing depth. If you want account aggregation or a long track record today, the premium DIY planners are strong, fair choices — and a spreadsheet still wins on raw flexibility.