Guide · Financial Calculator

Financial freedom calculator — find your FIRE number

Financial Independence, Retire Early — FIRE — is built on a single insight: if your investments can cover your living expenses indefinitely, you no longer need a pay cheque. Two numbers define your path: how much you need to save (your FIRE number), and how long it will take to get there. Pebble's financial calculator can answer both.

This guide walks through the 25× rule, shows how to use the TVM calculator to find your timeline, and explores what happens when you change your savings rate or starting balance. Whether you're targeting traditional retirement at 65 or an earlier exit, the math is the same.

Step 1: Find your FIRE number

The most widely used rule is the 25× rule, derived from the 4% safe withdrawal rate: a well-diversified portfolio should sustain a 4% annual withdrawal indefinitely, which means you need 25 times your annual spending saved before you can retire — at any age.

This is your target FV — the Future Value you're working toward. The lower your annual spending, the smaller your FIRE number and the faster you reach it. Reducing spending by $6,000 per year ($500/month) drops the FIRE target by $150,000 — a significant acceleration.

Lean FIRE vs Fat FIRE

Lean FIRE targets a minimal lifestyle — often $25,000–$40,000 per year — requiring a portfolio of $625,000–$1,000,000. Fat FIRE targets a comfortable or affluent lifestyle ($80,000–$120,000/year), requiring $2–3 million. Most people target something in between. Use your actual spending as the input, not an aspirational number.

Step 2: Calculate how long it takes

Once you know your FIRE number, the financial calculator tells you how many months of saving and investing it takes to get there. Here's the TVM setup:

• N — What you're solving for (months to reach FIRE)
• I/Y — Expected annual investment return (commonly 7% after inflation)
• PV — Your current invested savings (enter as negative)
• PMT — Monthly amount you invest (enter as negative)
• FV — Your FIRE number (enter as positive)

Investing $1,500 a month at a 7% average annual return, starting from zero, reaches the $1.2 million FIRE number in about 25 years. Over that time you contribute $450,000 yourself — compounding does the rest. See the compound interest guide for a deeper look at how this growth works.

What if you already have savings?

Already have $50,000 invested? Enter that as PV (as a negative number, since it's capital already at work) and watch the timeline shrink:

Starting with $50,000 already invested cuts about four years off the timeline — a vivid demonstration of why getting started early matters so much. Every dollar invested today has more time to compound than a dollar invested tomorrow.

Solving for monthly savings needed

Try solving for PMT instead: set N to your target timeline (say, 20 years = 240 months), plug in your current savings as PV and your FIRE number as FV, then tap CPT → PMT. The result tells you exactly how much you need to invest each month to hit your goal on schedule. From there, you can reverse-engineer a budget that makes financial independence a concrete, achievable plan — not just a dream.

The savings rate lever

The single most powerful variable in FIRE planning isn't your investment return — it's your savings rate. Higher returns help, but they're outside your control. Savings rate is within your control. Increasing monthly contributions from $1,500 to $2,000 (an extra $500/month) reduces the 25-year timeline to roughly 22 years. Increasing to $2,500/month brings it under 20.

Use the calculator iteratively: solve for N, adjust PMT upward, solve again. Each scenario takes seconds, and seeing the concrete timeline impact of each extra hundred dollars per month is one of the most motivating things you can do for your financial planning.

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