cFIREsim

Free browser-based FIRE retirement simulator

cFIREsim is a free online retirement calculator built specifically for FIRE (Financial Independence Retire Early) planning. The site declares "try it free, no account needed," and the simulator runs directly in the browser without requiring registration or payment. The tool uses two methodologies to test retirement scenarios: Monte Carlo analysis, which simulates random market returns, and historical-cycle analysis, which applies actual historical market sequences to your plan. Both approaches help surface how sensitive your retirement is to different market conditions and starting dates.

The simulator is maintained as a standalone website with no broker, lender, or financial advisor attached, and no affiliate relationships that would bias the tool toward particular institutions. A sister site called FIREproof handles more complex tax planning (federal and state income tax, capital gains, FICA, RMDs, IRMAA, 72(t) SEPP, and Roth conversion optimization), but that is a separate product. The core cFIREsim tool runs its own tax calculations as part of the simulation.

How money comes in

cFIREsim does not connect to banks or import account balances. The simulator is a projection tool, not a sync-based tracker. You enter your portfolio value manually at the start of your plan, and the tool models how that balance changes over time based on your inputs. The site does not describe integration with Plaid, direct bank connections, or automated imports. Your income sources, Social Security, pensions, annuities, or other income, are also entered by hand as line items you add to the simulation. The tool models when each income stream starts, how much it pays per year, and whether it adjusts for inflation.

When you set up a Social Security benefit, the simulator lets you specify the annual amount, the year you plan to claim, and whether the payment occurs annually or monthly. If you are married or have a dependent, you can model multiple Social Security streams. Pension and other income follow the same manual-entry pattern: you define the amount, the start year, the end year, and whether each adjusts annually for inflation. There is no real-time syncing or automatic refresh; the tool works only on the numbers you put in.

How the budgeting and simulation actually work

The simulator operates on a year-by-year cash-flow model. You input your portfolio balance, your annual spending, your portfolio allocation (as percentages across equities, bonds, fees, gold, and cash), and your expected investment return rate. The tool then models what your portfolio looks like at the end of each year, accounting for withdrawals and market growth. You can run multiple scenarios side-by-side for comparison: the interface lets you open a run of saved simulation tabs at once, each with its own set of assumptions, and warns you once you have reached the maximum number of open tabs.

One key workflow is testing different spending strategies. The site offers several options: inflation-adjusted spending (your annual withdrawal amount rises with general inflation), percentage-of-portfolio spending (you withdraw a fixed percentage of your current balance each year, sometimes called the 4% rule), and variable spending rules (VPW, Hebeler Autopilot, Guyton-Klinger, or variable CAPE). Each method changes how much you can safely spend year by year and how long your money lasts. You can also set spending floors and ceilings to cap your upside or protect a minimum lifestyle level.

The simulator accounts for Social Security, pensions, and other income as adjustments that reduce how much you need to withdraw from savings each year. It models a glide path if you want your portfolio allocation to shift gradually from aggressive to conservative as you near retirement. You can test early-retirement scenarios using historical data or constant-growth assumptions. The tool lets you set which historical period to test against (all available history, specific years, or a constant growth rate), which changes the sequence-of-returns risk the simulation exposes. The site emphasizes that you can run "what-if" scenarios and see year-by-year action plans, though the page does not spell out exactly what that action plan output includes.

What it costs and what it does not settle

cFIREsim is free. The site states plainly "try it free, no account needed." There is no paid tier, subscription, or one-time purchase. You do not provide an email, password, or sign-up credentials. The tool does not store your results or settings in the cloud; everything stays on your computer or device. If you close the page, your simulations are gone unless you manually save them.

What the site leaves open: it does not describe how accurate the historical data is, which time period the "all historical data" option covers, or how current the data is beyond a single line on the homepage stating "Most Recent Data: Aug. 1, 2026" and "Total Simulations Run: 37,132,049." It is not clear whether the historical returns include reinvested dividends, how the tool handles taxes on gains and income, or how often the historical dataset is refreshed. The site calls itself an educational tool and includes a disclaimer: "cFIREsim is not actual financial advice. Use this site as an educational application." This is important: the tool models scenarios but is not a substitute for personalized financial planning or tax advice.

Who it suits and who it does not

cFIREsim works well for FIRE planners who want to stress-test their retirement across different market scenarios without paying for a professional financial plan or advisor. The ability to run many scenarios side-by-side makes it useful for comparing strategies: seeing how delaying Social Security affects your plan, what happens if you work five more years, or whether a more aggressive portfolio allocation is necessary. It appeals to do-it-yourself planners comfortable entering their own numbers and interpreting results. The tool is also practical for couples planning jointly, allowing each partner to model different claiming strategies or spending approaches before deciding together.

The tool is less suitable for anyone who prefers automated bank syncing or who wants a long-term record of results in the cloud. It requires manual data entry for every financial variable, which means setup takes time and errors can happen if you mistype an amount or claim age. It is not a budgeting app for tracking actual spending; it is pure projection. If you need help categorizing current expenses or monitoring what you actually spend, you will need a separate tool. The simulator also assumes constant investment returns or historical returns, which may not match your portfolio's actual future performance or your behavior under market stress. Its strength is scenario exploration, not prediction.