cFIREsim and FI Calc vs MoneyVibe: historical backtests or worked answers
cFIREsim and FI Calc are free retirement simulators that replay your withdrawal plan through every period of US market history since 1871, using Robert Shiller’s data, and let you choose among many withdrawal strategies (FI Calc documents 13). MoneyVibe does not backtest. It works out the decisions around the withdrawal rate, such as the Roth conversion ladder, the ACA subsidy, 72(t) payments and withdrawal order, with the formula and sources on each page, and runs a seeded Monte Carlo for one portfolio. Use cFIREsim or FI Calc to stress-test a withdrawal rate; use MoneyVibe for the tax decisions that surround it.
We make MoneyVibe. We checked these details on October 1, 2026; tell us if something changed: Contact.
Side by side
| Compared | cFIREsim | FI Calc | MoneyVibe |
|---|---|---|---|
| Price | Free to use in the browser; the site shows no price.[1][2] | Free, supported by donations.[4] | Free.See About: the calculators stay free |
| Account needed | No log-in.[2] | No; you configure and run it on the page.[3] | No.See Privacy: no account, no login |
| Links to your bank | No; you type your numbers.[1] | No; you type your numbers.[3] | No.See Privacy: no bank or card details |
| How it tests a plan | Every historical period from 1871 (stocks, bonds, gold, inflation), updated from Shiller’s data; also constant growth or one chosen cycle.[2][1] | Historical backtest on Shiller’s annual data, 1871 through 2024.[6] | Monte Carlo: 5,000 seeded random paths from stated return and swing assumptions. No historical backtest.See Monte Carlo retirement success · Methodology: simulation |
| Withdrawal strategies | Eight spending plans, including VPW, Guyton-Klinger, Hebeler Autopilot and Variable CAPE, with floors and ceilings.[1] | 13 strategies, from constant dollar to Guyton-Klinger, CAPE-based and Vanguard Dynamic Spending.[7] | A constant inflation-adjusted withdrawal, and the order to draw from taxable, pre-tax and Roth accounts.See Safe withdrawal rate / how long money lasts · Tax-efficient withdrawal order |
| Social Security and other income | Yes: Social Security, pensions and other adjustments by year.[1] | Yes: wages, Social Security or other income.[3] | Social Security claiming age as its own calculator.See Social Security claiming calculator |
| Taxes, Roth ladder, ACA subsidy, 72(t) | Not in cFIREsim; its home page points to a sister site, FIREproof, for taxes, Roth conversions, 72(t) and ACA subsidies.[1] | Not in its documentation.[5] | Yes, one calculator for each.See Roth conversion ladder · ACA subsidy before Medicare · 72(t) SEPP |
| Sequence risk | Built in: every historical start year is its own sequence.[2] | Built in: every historical start year is its own sequence.[5] | Shown directly: the same returns in a different order.See Sequence of returns risk |
| Export | Each run gives a link to come back to it.[2] | CSV export and a share link.[3][5] | A copy-link button on each calculator; no CSV.See Monte Carlo retirement success |
| Visa: residency days, FBAR, PFIC, the 401(k) when you leave | Not among its inputs.[1] | Not in its documentation.[5] | Yes, one calculator for each.See US tax residency checker · FBAR / Form 8938 threshold checker · PFIC cost of home-country mutual funds · 401(k) withdrawal when leaving the US |
| Method explained | A long FAQ on the method and every input.[2] | Docs for each input, the data and each strategy.[5][7] | Formula, worked example, assumptions and dated sources on each tool page.See Methodology |
Each cFIREsim and FI Calc cell cites the page it comes from. Each MoneyVibe cell links to the live calculator or page that shows it. On a phone, swipe the table sideways.
Where cFIREsim and FI Calc are better
- Real history, not assumptions. Both replay your plan through every start year in the record, including the Great Depression and 1970s stagflation, using Robert Shiller’s data from 1871.[2][6] MoneyVibe’s simulator draws from stated averages and swings instead, and its methodology says that a normal distribution understates extreme crashes.
- Many withdrawal strategies. FI Calc documents 13, grouped into basic, spending-first and longevity-first;[7] cFIREsim offers eight spending plans with floors and ceilings.[1] MoneyVibe tests a constant inflation-adjusted withdrawal.
- Backtest depth. cFIREsim adds gold and cash, fees, glide paths and investigation options such as the highest spending that succeeded in every period;[1] FI Calc exports results to CSV for your own spreadsheet.[5]
- A long track record. cFIREsim’s counter showed more than 37 million simulations run when we checked.[1]
Where MoneyVibe fits
- The tax decisions around the withdrawal rate. A backtest tells you whether a spending level survived history. It does not tell you how much to convert to Roth this year, how much income keeps the ACA credit, or what a 72(t) plan pays before 59½. Those are Roth conversion ladder, ACA subsidy before Medicare and 72(t) SEPP.
- Plain language, every number shown. Each page leads with the answer, then the formula, a worked example with your inputs and dated sources.
- Sequence risk you can see. Sequence of returns risk puts the same returns in two orders side by side, which is the idea a backtest relies on, made visible.
Who should pick which
Pick cFIREsim or FI Calc to decide how much you can withdraw: test a spending level or a withdrawal strategy against every historical start year, and compare strategies. FI Calc is quicker to start; cFIREsim has more portfolio and adjustment options.
Pick MoneyVibe for the decisions that surround that number: conversions, the ACA cliff, early access before 59½ and the order to draw on accounts, with the math shown.
Use them together: settle the withdrawal rate in a backtester, then plan the tax side of drawing it here.
Questions
What is the difference between a historical backtest and a Monte Carlo simulation?
A historical backtest (cFIREsim, FI Calc) replays your plan through each real period of market history since 1871. A Monte Carlo simulation (MoneyVibe’s simulator) draws thousands of random return paths from stated averages and swings. Backtests use what happened; Monte Carlo can test sequences that never happened but depends on its assumptions.
Are cFIREsim and FI Calc free?
Yes. FI Calc says it is provided for free and supported by donations. cFIREsim runs in the browser with no log-in and shows no price. MoneyVibe’s calculators are free too.
Does MoneyVibe backtest against market history?
No. MoneyVibe’s simulators use 5,000 seeded random paths from stated assumptions, and its sequence-risk page is an illustration, not a historical backtest. For backtests, use cFIREsim or FI Calc.
Which tool should I use to pick a withdrawal rate?
Test the rate in a backtester such as cFIREsim or FI Calc, which also compare many withdrawal strategies. Then use MoneyVibe for the tax side: Roth conversions, the ACA subsidy, 72(t) payments and the order to draw on your accounts.
Try the calculators
- Safe withdrawal rate / how long money lastsHow much can I withdraw each year without running out?
- Monte Carlo retirement successWhat is the probability my plan survives volatility?
- Sequence of returns riskHow much does the order of returns change my outcome?
- Tax-efficient withdrawal orderWhich accounts to draw from first to minimise lifetime tax?
- Roth conversion ladderHow much to convert each year to access pre-tax money before 59½ at the lowest tax?
- ACA subsidy before MedicareWhat will health insurance cost until 65, and how do I keep MAGI under the cliff?
- 72(t) SEPPHow much can I take before 59½ without the 10% penalty?
- Social Security claiming calculatorWhen should I claim Social Security, and what will I actually get if I stop working early?
More in Retirement. Read the Library: Why Starting Early Matters (Retirement).
Sources
- cFIREsim, cFIREsim 3.0 (the simulator). Checked October 1, 2026.
- cFIREsim, About and FAQ. Checked October 1, 2026.
- FI Calc, FI Calc (the calculator). Checked October 1, 2026.
- FI Calc, About. Checked October 1, 2026.
- FI Calc Docs, Introduction. Checked October 1, 2026.
- FI Calc Docs, Historical Data. Checked October 1, 2026.
- FI Calc Docs, Withdrawal Strategies. Checked October 1, 2026.
We make MoneyVibe. We checked these details on October 1, 2026; tell us if something changed: Contact.