Lean FIRE Calculator

How soon could you reach financial independence if you adopted a leaner lifestyle with lower expenses? This calculator helps you estimate your FIRE number and project how many years it could take to get there.

Tip: Lean FIRE is mostly a spending game. Lowering annual spending does two things at once: it reduces your FIRE number and (often) increases your annual savings. Play with annual spending and savings to see how powerful that double effect can be.

Using this Calculator

This interactive calculator projects your invested net worth over time based on:

• Your current invested net worth
• How much you invest each year (annual savings)
• Your return + inflation assumptions (shown in today's dollars)
• Your target FIRE age (optional, used as the projection horizon)

The chart includes two lines:

• Net worth path: Your projected invested net worth over time
• FIRE target: Your FIRE number (the portfolio size that supports your spending)

To interact with the chart, hover over it to see values at each age.

What each line means

Net worth path: Your projected invested net worth as you continue investing each year.

FIRE target: The portfolio value required to support your desired annual spending using your chosen withdrawal rate.

What is Lean FIRE?

Lean FIRE is a version of FIRE (Financial Independence, Retire Early) focused on reaching independence with a lower-spending lifestyle.

There's no official definition, but the idea is:

• You aim for a smaller FIRE number
• You plan for a simpler lifestyle (often in a lower cost-of-living setup)
• You trade luxury for freedom (and usually reach independence sooner)

If you're new to FIRE, you may want to read: What is FIRE?

The FIRE number

This is THE number that matters in pursing financial independence. It's the size of the portfolio you need to support your desired retirement spending.

This calculator uses:

FIRE number = Desired annual spending ÷ Withdrawal rate

For example, if you want $40,000/year and you use a 4% withdrawal rate:

FIRE number = 40,000 ÷ 0.04 = $1,000,000

That means you'd aim for a portfolio around $1.0M (in today's dollars) before fully retiring.

Why Lean FIRE can be dramatically faster

The math behind Lean FIRE is what makes it so much faster than traditional FIRE.

Lowering spending accelerates FIRE because:

1. Your FIRE number gets smaller
2. Your annual savings often increases (if your income stays similar)

That's why small expense changes can create big timeline shifts.

"Today's dollars" and why the FIRE line is flat

This calculator expresses results in today's dollars, which makes the chart much easier to read.

To do that, it uses a “real return” approximation:

Real return ≈ Investment return - Inflation

This keeps the FIRE target from rising over time due to inflation, and makes the comparison across ages more intuitive.

(You can think of it as measuring purchasing power, not raw future dollars.)

Assumptions this calculator makes

To keep things simple and useful, the calculator makes a few assumptions:

• You invest your annual savings each year
• Your savings stays consistent in real terms
• The FIRE number is based on your desired annual spending and withdrawal rate
• Returns are smoothed to make the projection easier to understand

Who Lean FIRE is a good fit for

Lean FIRE can make sense if you:

• Value freedom more than luxury spending
• Have (or want) a simple lifestyle
• Want to reduce required portfolio size
• Are willing to optimize housing / transportation / recurring expenses
• Are comfortable building flexibility into your plan

It can be especially compelling for people who are burnt out and want an earlier “escape hatch,” as long as the lifestyle feels sustainable.

Tips for making Lean FIRE work

Here are the biggest levers that change your result:

Lower annual spending
This reduces your FIRE number directly.

Increase annual savings
More contributions = faster compounding.

Use conservative assumptions
Try a lower return and/or lower withdrawal rate to see a safer scenario.

Plan for lumpy costs
Healthcare, housing changes, and life events can shift spending. If you're not sure, pad your spending estimate.

Build optionality
Even a small amount of side income or part-time work can dramatically improve safety and flexibility.

Frequently Asked Questions (FAQs) About Lean FIRE

Is Lean FIRE the same as Coast FIRE?

• No, they're related, but different.

• Lean FIRE: You reach full FIRE but with lower spending.

• Coast FIRE: You have enough invested that you could stop contributing and still hit full FIRE later.

Many people use both ideas together: reach Coast FI early, then pursue a leaner spending target.

Why does the calculator only show one FIRE target?

• In reality, the math is the same between Lean FIRE, Traditional FIRE, and even Fat FIRE. The only difference is the spending target you choose.

What withdrawal rate should I use?

• Many people use 4% as a starting point, but your situation might call for a lower or higher rate depending on time horizon and flexibility.

• A lower withdrawal rate increases your FIRE number while a higher one decreases it.

Does this include taxes?

• No. This is a simplified planner. Taxes, healthcare costs, Social Security, and other real-world factors can materially change results. Use this calculator as a starting point to build your more in-depth plan.

Does it assume my expenses stay the same forever?

• The chart uses today's dollars and assumes spending is stable in real terms.

• In reality, spending often changes over time. If you want to be conservative, increase your desired annual spending.