Each scenario runs 10,000 independent simulations of your financial future. Every simulation draws random annual market returns from a distribution calibrated to historical equity performance, including skewness. The result is a probability distribution of outcomes — not a single projection.
Dual-tax modeling currently activates only for US citizens living outside the US. The simulator computes residency-country tax and US citizenship tax separately, then applies a simplified foreign tax credit within each income category so the net tax reflects the larger of the two when both sides tax the same category.
The treaty layer currently covers eighteen US-citizen residency pairs: Australia, Austria, Belgium, Canada, Cyprus, France, Germany, Greece, Italy, Japan, Malta, Mexico, Netherlands, Portugal, Spain, Switzerland, Thailand, and the UK. The matrix can override Social Security, public pensions, private pensions, traditional IRA/401(k) withdrawals, Roth withdrawals, and capital gains. The clearest treaty differences today are Social Security; public-pension rows use source/payor-state routing only where the model's combined bucket aligns with the cited treaty rules. Categories that remain subject to savings-clause, Roth-recognition, lump-sum pension, treaty-cap, or government-service ambiguity fall back to the default FTC path.
Primary treaty sources are the IRS country treaty document pages and treaty or Treasury technical-explanation PDFs, starting from the IRS treaty A-Z list. New rows cite the IRS pages for Austria, Belgium, Cyprus, Greece, Malta, Mexico, Netherlands, Switzerland, and Thailand.
This remains intentionally simplified. FEIE is not modeled, and treaty elections, limitation-on-benefits clauses, and article-by-article savings-clause exceptions are not modeled. Portugal NHR legacy retirement-withdrawal handling also remains a specific simulator assumption.
U.S. state tax after emigration. When the U.S.-citizen overlay is active for a residency outside the United States, the simulation models U.S. federal tax with no ongoing state-tax overlay — even when the saved scenario still advertises a high-tax last state. Sticky-state domicile rules can keep prior residents on the state-return hook in fact-specific cases, but inferring continued residency from the saved U.S. state would turn an unresolved legal question into a hidden tax assumption. A user-editable continued-state-residency overlay is intentionally out of scope here.
Roth and other tax-free wrappers abroad. Given these assumptions, Roth IRA, Roth 401(k), and other U.S. tax-free wrappers are modeled as locally taxable by default in the residency country. The simulator only treats a Roth withdrawal as locally exempt when the cross-border registry encodes a source-backed country-specific exception for that residency (for example, the Canada and U.K. rows). When no such row exists, the simulation assumes the residency country taxes the withdrawal as ordinary local income — the conservative fallback — rather than inferring local tax-free status from the U.S. wrapper label.
Selecting Country = X means the simulation models the ordinary tax-resident profile of that country — standard bracket-based income tax plus the country’s default investment, gains, and wealth treatment for a resident individual. Special regimes (NHR, IFICI, non-dom, remittance basis, pensioner flat tax, LTR, etc.) are explicit assumptions only: they apply when the user picks them via the tax-regime selector, and never as a silent default inferred from country alone. Where a regime is not yet modeled, the simulation lists it as a simplifying assumption rather than treating it as the default.
The simulation assumes ordinary domiciled Cyprus tax resident as the default. Portfolio dividends and interest are modeled separately from capital gains: the default profile applies the Special Defence Contribution (SDC) layer to portfolio dividends and interest at 17%, while standard financial-portfolio capital gains are modeled at 0%. Selecting the non-dom tax-regime is an explicit assumption that removes the SDC layer for up to 17 years of Cyprus residence. Cyprus immovable-property capital gains are source-specific and are not modeled in this simplified profile.
The simulation assumes ordinary worldwide Malta tax resident as the default, taxing portfolio dividends and interest under the standard final-withholding layer regardless of source. The non-dom remittance-basis regime is an explicit assumption only. Given the FIRE remittance assumption, non-dom + foreign-source taxable portfolio income used for spending is modeled as remitted in-year and therefore taxed locally; foreign capital gains are modeled separately from foreign income and remain generally exempt for individuals on financial-portfolio gains. Malta non-dom does not auto-exempt foreign investment income that funds your withdrawals.
For 2026, the simulation models ordinary Thai tax resident on a worldwide basis (Thailand transitioned from pure remittance to worldwide effective 2024). Foreign-source taxable portfolio dividends and interest used to fund spending are assumed remitted in-year and taxed under the resident schedule (10% on dividends, 15% on interest as the modeled withholding layer). Realized financial-portfolio capital gains are currently modeled at 0% as a simplification that broadly applies the Thai-listed-securities capital-gains exemption; this is a known gap, since the listed-securities rule is domestic-source under Thai law and would not automatically extend to foreign brokerage gains. Source-aware foreign-CG treatment would require a follow-up spec that tags portfolio gains by source and taxes foreign gains under the worldwide resident schedule. The Long-Term Resident (LTR) visa regime is not modeled; it would only apply if added as an explicit tax-regime selection in a later spec.
For Mexico residency with U.S. citizenship, the approved default is full Mexican tax residency plus the U.S. citizenship overlay. The simulation runs the SAT resident tariff on ordinary income, models dividends and listed-share gains at the simplified 10% layer, and then applies the standard U.S. dual-tax overlay with foreign tax credit at the income-category level. The U.S./Mexico treaty’s pair-specific carve-outs are not yet encoded in the matrix, so categories without a source-backed row fall back to the default both + FTC path. Mexican social-security routing, asset-by-asset source tracing, and article-level treaty optimizations are documented as out of scope for this simplified profile.
The simulation assumes ordinary Portuguese tax resident as the default, with portfolio dividends, interest, and taxable financial-portfolio gains modeled at the ordinary 28% autonomous rate. NHR, IFICI, and the optional englobamento (progressive aggregation) election are explicit assumptions only — they apply when the user picks them via the tax-regime/englobamento selectors and never as a silent default. There is no automatic “lower of autonomous vs. progressive” choice; the year-by-year tax detail names the elected method when englobamento is on.
The simulation assumes ordinary Spanish tax resident as the default. The autonomous-community selector stays visible because regional rules materially affect both ordinary-income surcharges and wealth tax — the default regional profile is one choice among several, not a universal Spanish baseline. Primary residence value and outstanding secured debt are exposed as separate Tax & Location Details inputs and feed the wealth-tax calculation directly. The habitual-residence wealth-tax exemption is modeled as capped at EUR 300,000 per taxpayer (a couple with both names on the title can apply the per-taxpayer cap once each, rather than the cap doubling for a single filer). The national solidarity tax is included as a simplification on top of the regional wealth-tax schedule rather than as a fully community-by-community computation.
The simulation assumes ordinary French tax resident as the default, with the PFU (prélèvement forfaitaire unique) as the default investment treatment for portfolio dividends, interest, and taxable securities gains at 31.4% (12.8% income tax plus 18.6% social levies). The optional progressive barème election is not modeled unless a future spec exposes it as an explicit selector. For France + U.S. scenarios, U.S. retirement wrapper treatment follows the cross-border registry: U.S.-source Social Security routes to the U.S./payor side, traditional IRA/401(k)-style withdrawals are modeled as French private-retirement income on the residence side with the U.S. citizenship overlay still applying via FTC, and Roth withdrawals follow the conservative locally-taxable default because no source-backed France Roth exception is encoded.
The simulation assumes ordinary Italian tax resident as the default. Domestic financial portfolio income and realized gains are modeled under the flat 26% substitute-tax treatment rather than aggregated into IRPEF. The recurring annual financial-asset charge (stamp-duty / IVAFE-style) is applied as a taxable-portfolio-only simplification: it runs against taxable brokerage / taxable financial-portfolio balances at 0.2% per year, and is not applied to primary residence, other real estate, tax-deferred accounts, Roth/tax-free accounts, or special-regime balances. The Italian pensioner-flat-7% regime is an explicit assumption only and applies only when selected via the tax-regime control.
Across all non-U.S. residencies for U.S. citizens, two assumptions apply uniformly: (1) the simulation models no ongoing U.S. state tax after emigration, even if the saved scenario still references a prior high-tax state, and (2) Roth IRA, Roth 401(k), and other U.S. tax-free wrappers are modeled as locally taxable by default unless the cross-border registry encodes a source-backed country-specific exception (such as the Canada or U.K. Roth rows). Sticky-state residency facts and country-specific Roth recognition are real but unresolved questions; the simulation treats them as user-editable future overlays rather than hidden defaults.
Tax calculations use bracket-based models for income tax, capital gains tax, and wealth tax where applicable. Each supported country has its own tax module reflecting current published rates and thresholds. Tax models are simplified approximations — consult a qualified tax professional for your specific situation.
Default return parameters are calibrated to long-run global equity performance. Returns are modeled as log-normal with an adjustable skewness factor to capture fat-tail risk.