Guide · Financial Calculator

How to calculate your path to financial freedom

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.

Step 1: Find your FIRE number

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

Annual spending × 25 = FIRE number

$48,000 × 25 = $1,200,000

If you spend $48,000 per year, you need $1.2 million invested

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.

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 setup:

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

Example: starting from scratch, $1,500/month invested

I/Y = 7

PV = 0

PMT = −1,500

FV = 1,200,000

Result → N ≈ 299 months (~25 years)

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.

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:

Example: $50,000 already invested, $1,500/month going forward

I/Y = 7

PV = −50,000

PMT = −1,500

FV = 1,200,000

Result → N ≈ 255 months (~21 years)

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.

Adjusting your variables

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.

Open the Financial Calculator →