There’s no single best free FIRE calculator, because each one answers a different question. FIRECalc and cFIREsim test whether a portfolio would have survived every stretch of U.S. market history. Networthify gives you a fast “years until I can retire” from your savings rate. Retire Goals tracks your progress on your phone and turns it into a projected date with Monte Carlo odds. Most people end up using a backtester for the big decision and a tracker for the years in between.
Here’s what each tool does well, where it falls short, and who it suits.
The best free FIRE calculators compared #
| Tool | Where | Answers | Method | Best for |
|---|---|---|---|---|
| FIRECalc | Web | Would my money have lasted? | Historical backtest since 1871 | A quick survival check before retiring |
| cFIREsim | Web | How do different spending rules hold up? | Historical data or constant growth | Detailed drawdown planning |
| Networthify | Web | How many years until I can retire? | Fixed return, savings-rate math | A fast first estimate |
| Retire Goals | iOS and Android app | When will I reach my goal, and what are the odds? | Compound projection plus Monte Carlo | Tracking progress over years |
FIRECalc: the classic survival test #
FIRECalc asks one question: with what you have and what you spend, can you retire? It runs your plan through every starting year in its U.S. data, back to 1871, and reports how often your money would have lasted. As the site puts it, if your strategy survived the Great Depression, 1970s inflation and every other calamity in that record, it’s likely to survive what comes next.
Limits: it’s a drawdown tool, so it tells you little about the saving years. The data is U.S.-only and the interface is dated.
cFIREsim: the detailed simulator #
cFIREsim also uses historical data, with more controls. You can choose among spending strategies (inflation-adjusted, variable spending, variable percentage withdrawal, Guyton-Klinger guardrails and others), set spending floors and ceilings, add Social Security or pension income, and build a glide path that shifts your allocation over time. It also offers constant-growth runs if you want a simple projection.
Limits: lots of inputs, so it’s easy to over-tune. Like FIRECalc, it’s built around U.S. history, and it says plainly that it’s an educational tool, not financial advice.
Networthify: the fast first estimate #
Networthify’s early retirement calculator takes after-tax income, savings, expenses, portfolio value, an after-inflation return and a withdrawal rate, and tells you how long until your investments cover your spending. It’s the fastest way to see how much your savings rate matters.
Limits: it assumes retirement spending equals today’s spending and that you live only on returns without drawing down principal. It uses one fixed return, so there’s no sense of how market swings could change the answer.
Retire Goals: the tracker with odds #
Retire Goals is a phone app rather than a one-time calculator. You set goals from templates (FIRE, 401(k) with employer match, Roth IRA, index fund, dividends and others), log contributions as you make them, and each goal shows a projected finish date, a growth curve and milestones at 25%, 50%, 75% and 100%. Its Monte Carlo outlook runs the plan through hundreds of randomized return sequences and reports the probability you reach your target. Five calculators are built in: compound growth, FIRE number, Coast FIRE, dividend income, and Will My Money Last for the drawdown phase.
It’s free with a small banner ad. A one-time Pro upgrade removes ads and adds the full projection range on every goal. There’s no account, data stays on your device, and it never connects to your bank; you enter contributions yourself.
Limits: no historical backtesting, no Social Security or pension modeling, and no tax calculations. It won’t import balances automatically, which is a privacy choice but means a few seconds of typing per contribution.
Monte Carlo vs historical backtesting: which should you trust? #
Both, for different reasons.
- Historical backtesting (FIRECalc, cFIREsim) replays real sequences: the 1929 crash, 1970s stagflation, 2008. It’s concrete, but there are only about 150 years of U.S. data, so there are few truly independent 30- or 40-year periods to learn from.
- Monte Carlo simulation (Retire Goals) generates many random return sequences from an average and a level of volatility. It can produce bad sequences history never showed, but its results depend on the assumptions behind the randomness.
A plan that passes both is on solid ground. For a deeper walkthrough, see how to run a FIRE retirement simulation.
Which inputs matter most? #
Every calculator is only as good as what you type in. Four inputs move the answer most.
Savings rate #
Starting from zero, with a 5% real return and a 4% withdrawal rate:
| Savings rate | Years to financial independence |
|---|---|
| 10% | about 51 |
| 30% | about 28 |
| 50% | about 17 |
| 70% | about 9 |
Expected return #
Use a real (after-inflation) return. The S&P 500’s long-run nominal average is around 10%, but planners often use 5% to 7% real to leave room for bad decades. Our guide on what S&P 500 return to use for retirement planning goes through the options.
Withdrawal rate #
The 4% rule came from research on 30-year retirements. Early retirees planning for 40 or 50 years often use 3.25% to 3.5%. See whether the 4% rule holds up for a 40-year retirement.
Retirement spending #
Don’t just copy today’s budget. A paid-off mortgage lowers it; buying your own health insurance before Medicare raises it; more free time often means more travel. Our guide to calculating your FIRE number covers building that figure.
Which calculator fits your FIRE style? #
- Lean or traditional FIRE: Networthify for the first estimate, then FIRECalc to check the drawdown survives.
- Fat FIRE: cFIREsim, because flexible spending rules matter more when a lot of your budget is discretionary.
- Coast FIRE: a Coast FIRE calculator, such as the one in Retire Goals, which finds the balance that grows to your FIRE number with no new contributions.
- Barista FIRE: cFIREsim can add part-time income as a separate stream; Retire Goals lets you track a Barista target and a full FIRE target side by side.
Frequently asked questions #
Is the 4% rule still safe for early retirement? #
It’s a reasonable starting point, not a guarantee. The original research covered 30-year retirements, and a 45-year retirement has more ways to go wrong. Many early retirees plan on 3.25% to 3.5%, or use a flexible rule that trims spending after bad years.
Do free FIRE calculators include taxes? #
Most don’t calculate taxes for you. The simplest fix is to estimate your retirement taxes separately and add them to your annual spending before running any calculator.
Do I need to link my bank account to use a FIRE calculator? #
No. FIRECalc, cFIREsim and Networthify take numbers you type in. Retire Goals also works without any bank connection or account; you log contributions yourself and the data stays on your phone.
How often should I update my retirement projections? #
Log contributions as you make them, and do a full review once or twice a year or after a big change like a new job, a move or a child. Checking projections daily mostly produces anxiety, because short-term market moves barely change a plan measured in decades.