The FI Calculator

The FI Calculator is a free, browser-based tool for mapping out a path to Financial Independence and Retire Early, built as a single dedicated calculator on its own domain. Running entirely in your browser with no signup or bank connection required, it serves both desktop and mobile users. The site also offers an optional "AI Retirement Bot" companion built on ChatGPT, launched in March 2026, which helps interpret results and model scenarios conversationally by discussing your plan in natural language. The core calculator is free and requires no account; the bot is accessed through ChatGPT's platform separately. The tool targets the FIRE community, people researching early retirement strategies, and anyone wanting to model long-term wealth accumulation without external advisors. A "Buy me a coffee" donation button appears for users who find the tool valuable enough to support its development and server costs.

Money flows entirely through manual entry. There is no bank sync or automatic transaction import. You enter your current age, gross annual income, expected annual salary increases as a percentage, and your net yearly savings contribution (the total you add to savings after taxes, including 401k and IRA contributions). You also specify your desired yearly retirement expenses in today's dollars, any monthly income you expect after FIRE (such as pensions, rental income, or part-time work), and your chosen safe withdrawal rate, defaulting to the widely recommended 4 percent. The page explains that the 4 percent rule derives from the Trinity Study, which found that a 4 percent annual withdrawal rate had a 100 percent success rate over a 30-year retirement horizon when applied to a 50 percent stock, 50 percent bond portfolio. The tool defaults pre-FIRE investment returns to 10 percent (the S&P 500 historical average since inception) and post-FIRE returns to a more conservative assumption. All figures adjust automatically for inflation you specify, defaulting to 3 percent annually, the historical US average.

The calculator then builds your projection step by step across multiple output sections. Its "Your Financial Snapshot" input section asks for current savings balance, desired retirement expenses, and monthly income after FIRE. Beyond the basics, you can add one-time or recurring cash flows: major expenses like college costs, inheritances, pensions, or other income streams, each spanning years you define. The results display your Adjusted FIRE Number (savings needed to cover non-pension expenses), Time to FIRE, Age at FIRE, FI Date (calendar date when you reach your number), Savings Rate as a percentage of gross income, Years of Expenses Covered (how long your current savings would sustain you), Total Contributions to FIRE, and Total Growth to FIRE (the investment gains). A detailed year-by-year table breaks down starting savings, contributions made that year, investment growth in real (inflation-adjusted) dollars, any life events that year, and ending savings. For those considering Coast FIRE (stopping contributions early and letting existing savings compound), a separate Coast FIRE Number section (improved as of April 12, 2026) shows what you need invested by your Coast Age to reach FIRE by your Target Age with no further savings, plus a full table showing how your money grows through the coasting period.

The site includes a "Time-Cost Translator" tool that translates purchases into years of extra working time. Enter a one-time purchase, daily habit, weekly expense, monthly subscription, or yearly recurring amount, and the calculator shows how many years earlier (or later) you could retire if you skip it. The advanced section offers two distinct simulation engines for stress-testing your plan against market uncertainty. Historical Cycles replays the last century of actual market data (including every major crash and boom from 1928 to 2023) to show how your plan would have fared through real history. Monte Carlo generates thousands of unique random futures based on your assumed average returns and specified market volatility, letting you test "what if the future unfolds as uncertain as I expect?" Both simulations let you set your stock/bond allocation, specify spending flexibility rules (automatically reduce spending if your portfolio drops below its starting value by a certain threshold to help it recover faster), and display your success rate (the probability of your money lasting to age 95), median final portfolio value at age 95, and the 10th and 90th percentile outcomes to show best-case and worst-case scenarios. Currency support includes USD, EUR, CAD, SGD, GBP, JPY, AUD, CHF, HKD, INR, TWD, and VND, making the calculator accessible to international FIRE planners.

The calculator is entirely free with no paid tiers, no advertising, and no pricing model mentioned. The interface stores nothing on any server, running entirely in your browser for privacy. Recent updates (as of April 2026) added dark mode toggle with automatic browser storage, so your inputs persist between sessions without re-entry, and a data export function lets you download your calculations and assumptions as a file. Coast FIRE simulation tools improved in April 2026 to show the exact date you can stop saving while still reaching FIRE through compounding alone, with a full pre-coast accumulation table plus a post-coast table showing years of no-contribution growth. The AI Retirement Bot (launched March 30, 2026) now models the true cost of daily habits (translating a coffee habit into retirement years), simulates market crash scenarios (showing how your plan survives downturns), and discusses major life events conversationally, helping you understand how changes affect your timeline and success rate. The tool also includes a print summary feature so you can document your plan in hard copy or PDF, and links to related planning content including a FIRE guide for newcomers and blog posts on topics like the "One More Year" strategy and spending cuts' impact on success rates.

The FI Calculator suits anyone planning retirement decades away who wants to control exactly what assumptions feed their projections and stress-test them against historical and random futures. The manual-entry model means you own your assumptions entirely, and the dual simulation engines let you explore real market histories and probabilistic scenarios side by side. It does not suit those needing ongoing rebalancing advice, tax-loss harvesting guidance, help selecting specific investments, or direction on which accounts to fund first. It is a planning tool for exploring "when can I retire," not a portfolio manager or financial advisor. The site includes a clear disclaimer that results are for informational and illustrative purposes only and do not constitute financial, investment, or tax advice. The community resources listed on the site (The Simple Path to Wealth, The Psychology of Money, Die With Zero) suggest an audience comfortable self-directing their investment strategy once the numbers show them their FIRE date.