Ifso runs your income, accounts and expenses forward to age 90, letting you drop decisions onto the timeline — “buy a house at 31,” “retire at 55” — and click any year to edit what happens then. It models federal and state tax brackets, 401(k)/IRA limits, mortgage amortisation, capital-gains tax with the primary-residence exclusion, and Social Security claim-age adjustments, then a Monte Carlo mode reruns the plan under varying returns and reports how often it holds. Free, US tax model only; Pro is $9/month.