If you're planning for early retirement or financial independence, The fire calculator can be your best friend. This online tool helps you model your financial future by using real data and realistic simulations. But to get the most accurate results, you need to input your data correctly. In this guide, we’ll walk you through exactly how to use The fire calculator — step by step — so you don’t miss anything important.



This tutorial is written in simple words, so whether you’re just starting your FIRE journey or you’re already a seasoned saver, you’ll understand every part. Let’s get started.



What Is The Fire Calculator?

Before we dive into the tutorial, let’s quickly explain what The fire calculator is. It’s a free online tool designed to help people calculate when they can retire — especially those aiming for FIRE (Financial Independence, Retire Early). Unlike basic retirement tools, this one uses Monte Carlo simulations, which means it tests thousands of possible futures based on the numbers you enter.



This helps you see not just a single outcome, but many. It tells you how strong or fragile your retirement plan really is.



But to make sure the results are useful, you need to enter the right data in the right way.



Why Inputting the Right Data Matters

When you use any financial tool, the quality of your results depends on the quality of your inputs. Think of it like baking a cake. If you leave out the sugar or guess the temperature, the cake won’t turn out well.



The same goes for The fire calculator. If you guess too much or miss key details, your results might look better or worse than they really are.



That’s why this step-by-step tutorial is so important. We’ll guide you through every input field — and explain what each one means — so you feel confident and in control.



Step 1: Go to The Fire Calculator Homepage

When you first arrive at the calculator, you’ll see a set of input boxes on the left-hand side. This is where you’ll enter your personal financial data.



Don’t worry — you don’t need to be an expert. Just be honest with your numbers, and the calculator will do the heavy lifting.



Step 2: Input Your Age and Retirement Age

Current Age

Enter your age right now. For example, if you are 35 years old, just type 35.



Retirement Age

Enter the age at which you want to stop working full time. This could be 40, 50, 60 — whatever your FIRE goal is.



These numbers help the calculator figure out how many years you’ll be saving and how many years you’ll be living off your savings.



Step 3: Enter Your Current Portfolio Size

Portfolio Size

This is how much money you already have invested. Do not include your house or car. Only count things like:



Stock market investments



Retirement accounts (401(k), IRA, etc.)



Brokerage accounts



Cash savings set aside for retirement



If you have $100,000 saved in total investments, enter 100000.



This is the foundation of your FIRE journey, so try to be as accurate as possible.



Step 4: Input Annual Contributions

Annual Contribution (before retirement)

This is how much money you save and invest each year before you retire.



Example: If you save $1,500 each month, that’s $18,000 per year. Enter 18000.



Be sure to include all contributions — from your salary, side hustle, business, etc.



Step 5: Input Annual Spending (After Retirement)

Annual Spending

This is the amount of money you expect to spend each year after you retire.



Include:



Rent or mortgage



Food



Travel



Insurance



Medical bills



Entertainment



Any other lifestyle costs



If you expect to spend $30,000 a year during early retirement, enter 30000.



Be realistic. Don’t guess low just to make the calculator say what you want to hear.



Step 6: Set Your Expected Market Returns

Return Rate (average annual return)

This is how much you expect your investments to grow each year, on average.



A common estimate is 7% per year, based on the historical stock market average (after inflation). But if you’re more conservative, you could enter 5%.



Standard Deviation (volatility)

This shows how “bumpy” the market is — how much it goes up and down.



A typical value is 15% for a stock-heavy portfolio.



The fire calculator uses these numbers to create thousands of simulated market paths, including crashes and booms.



Step 7: Select the Number of Simulations

You’ll usually see a field for how many Monte Carlo simulations you want to run. More simulations = more accurate results.



A good number is 10,000 simulations. This gives you a strong picture of what might happen in both good and bad markets.



Step 8: Run the Simulation

After entering all your data, click the button to run the simulation.



In just a few seconds, you’ll get powerful results.



Step 9: Understand Your Results

Once the simulation finishes, you’ll see a few important numbers and charts.



Success Rate

This is the percentage of simulations where you don’t run out of money before the end of retirement.



90–100% = Very strong plan



75–89% = Okay, but could use improvement



Below 75% = Risky, may need adjustments



Portfolio Graphs

You’ll see colorful charts showing how your portfolio could grow or shrink in different futures. Some lines go up sharply, others crash and recover, and some run out of money.



These are real possibilities — and they help you see how flexible your plan really is.



Step 10: Try Different Scenarios

Don’t stop at one result. Change your numbers and see how it affects the outcome.



Try these:



Retire 2 years earlier



Save $5,000 more per year



Spend $3,000 less in retirement



Use a lower return rate (5%)



Simulate a market crash by increasing volatility



Each change shows you how safe or risky your plan is. The goal is to create a plan that still works in tough times — not just in perfect ones.



Tips for Inputting the Right Data

Here are some simple but powerful tips to help you get the best results from The fire calculator:



1. Don’t Be Overly Optimistic

It’s tempting to assume high returns or low spending. But being too optimistic can lead to failure later. Use realistic numbers — or even slightly conservative ones.



2. Update Your Numbers Every Year

Your finances change. Maybe you get a raise, your spending increases, or the market changes. Re-run the calculator once or twice a year.



3. Include Extra Income If You Plan on Working Part-Time

If you plan to work part-time after early retirement (like Barista FIRE), include that income as a reduction in your spending.



4. Account for Inflation

The calculator works in today’s dollars, so think about what your spending means today — not in 20 years. That keeps things simple.



Example Walkthrough

Let’s go through a full example using simple numbers.



Age: 30



Retirement Age: 45



Current Investments: $150,000



Annual Savings: $25,000



Annual Spending After Retirement: $35,000



Expected Return: 7%



Volatility: 15%



Simulations: 10,000



When we run this, the success rate might be around 85%.



Now let’s make a few changes:



Lower spending to $30,000



Add 3 more years of saving (retire at 48)



The new success rate could jump to 95–97%. That’s a big improvement — and it shows how powerful small adjustments can be.



Common Mistakes to Avoid

Avoid these common errors when entering your data:



Forgetting taxes: If your retirement income is taxable, adjust spending upward slightly.



Underestimating spending: Be honest. It's better to be safe than sorry.



Overestimating returns: The market doesn’t grow 10% every year. Stick with 5–7%.



Leaving out contributions: Don’t forget employer matches or side income.



Ignoring future changes: Your life might change — plan for flexibility.



Final Thoughts: Practice Makes Progress

The fire calculator is a powerful, free tool that can change your financial future — but only if you use it correctly. By following this step-by-step guide, you’ll know exactly how to enter your data the right way.



Keep experimenting. Try different scenarios. Run new simulations each year. The more you use the tool, the better you’ll understand your plan — and the more prepared you’ll be.



Financial freedom doesn’t happen by accident. It happens by planning, testing, adjusting, and staying consistent.



So go ahead — input your real numbers, stress test your plan, and use The fire calculator to build the future you want.